Class 8

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 9 Disaster Management Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 9 Disaster Management

Class 8 Science Chapter 9 Disaster Management Textbook Questions and Answers

1. Answer the following in your own words.

Question a.
Explain the relation between continuous rains and landslide. Give reasons.
Answer:
Before the actual landslide, many changes occur in the surrounding hilly ground. The hard rocks develop cracks and crevices. These are natural changes but due to man-made activities, the cracks are widened due to erosion. These cracks make the big rocks to break into smaller stones. The cracks widen further due to excessive rainfall. These rocks further get eroded and they fall down along with soil from the slopes. The entire process is speeded up due to rainwater.

Question b.
Prepare a chart showing ‘Dos’ and ‘don’ts’ at the time of earthquake.
Answer:
At the time of earthquake

Question c.
What are the specifications of an earthquake-proof building?
Answer:
The earthquake-proof building is such that even if the earthquake is caused, it should not cause damage to the buildings due to these earth movements. There are some codes of conduct while constructing such buildings. Advanced technology is used for earthquake resistant construction. The foundation of earthquake-proof building is separated from lower land. The walls are of less weight or they are wooden. The house constructed with special light materials are preferred in earthquake-prone regions.

Question d.
Explain the effects of landslide.
Answer:
1. Mostly rivers originate in the hills and mountains. When there is landslide, the rivers naturally get flooded.
2. The paths of the riverine water changes due to landslide.
3. Waterfalls are displaced from their original positions.
4. New and artificial water reservoirs are created.
5. The falling debris, soil and rocks make the trees at the base of hillside uprooted. All the plant life is lost.
6. The constructions done by the villagers on the slope can be totally damaged due to landslide. There is large scale damage to property and life. In few cases like Malin the entire village was buried due to landslide and accompanied rainfall.
7. Transportation is affected as the roads and railway tracks are blocked due to debris.

Question e.
Is there any relation between dam and earthquake? Explain.
Answer:
There is abundant water stored in the dams. This water column puts additional weight on the ground. Initially there may not be any weight, but later due to construction of dam, suddenly the pressure of this weight is so high that this ground experiences the tension. If such area is already earthquake-prone, then there can be chances of earthquake. According to theory of plate tectonics, there are continuous movements in the earth’s surface. If over such fragile plates, the dams are constructed then the chances of earthquake are enhanced.

2. Give Scientific reasons.

Question a.
It is safer to find shelter under things like a bed, table at the time of earthquake.
Answer:
When earthquake takes place, due to the vibrations in the earth’s surface, there is possibility of the roof and walls of the house to fall. This collapse can cause severe head injury which can be fatal. Thus, one must take shelter below the hard-supporting structures such as bed or table. This precaution can save one’s life.

Question b.
In monsoon, don’t take shelter near hillside.
Answer:
The excessive rainfall can cause landslides. The soil and rocks from the hillside can be pushed down along with the flow of rainwater. This debris slides to the lower heights from the hills. This explains us that taking shelter near the base of the hillside can be disastrous as one can be buried in the debris due to sudden landslide. Therefore, in monsoon, one should not take shelter near hillside.

Question c.
Don’t use lifts at the time of earthquake.
Answer:
Lifts or elevators run on electricity. The electricity supply can be hindered due to earthquake. There may be chances of fire due to short circuit. We may get trapped in the elevator at such times. The building may also collapse due to earthquake. It is always better to use stairs at the time of such calamities, so that one can safely come out of the building. Therefore, it is said that lifts should not be used at the time of earthquakes.

Question d.
The foundation of earthquake- proof building is separated from lower land.
Answer:
The surface of the earth trembles at the time of earthquake. These tremors cause seismic waves which are responsible for the movements of the earth’s surface. The ground thus shakes or it goes up-down. These shocks and waves formed in the interior of the earth spread on the surface in all directions. This causes collapse of the building and other structures on the land.
To prevent such disasters the foundation of earth-quake proof building is separated from lower land.

3. If a crowd gathers at the place of earthquake, what would be the difficulties in relief work?

Question a.
If a crowd gathers at the place of earthquake, what would be the difficulties in relief work?
Answer:
If people flock in crowd, the rescue work will not be possible. The ambulances and the fire engines will not reach the spot where the help is needed. The personnel from disaster management cells cannot thus act in time. It will be difficult to manage the situation and thus such crowding should never be done.

4. Make a list of the institutes and organizations who provide help for disaster managment. Collect more information about their work.

Question a.
Make a list of the institutes and organizations who provide help for disaster management. Collect more information about their work.
Answer:
International government organisations working for disaster management are:
a. The United Nations and its organisations:
1. The Food and Agricultural Organisation of the UN (FAO): It gives early warning of impending food crises, and keep track of global food supply problems.
2. The United Nations Development Programme (UNDP): It helps disaster-prone countries with disaster mitigation, prevention and preparedness measures.
3. The World Food Programme (WFP): It is the main supplier of relief food aid.
4. The World Health Organisation (WHO): It gives global public health leadership by setting standards, monitoring health trends, and providing direction on emergency health issues. WHO’s role is to reduce avoidable loss of life and the burden of disease and disability.

b. The International Committee of the Red Cross ( ICRC): It gives physical rehabilitation to people injured by explosive weapons or other types of incident.

c. The International Federation of Red Cross and Red Crescent Societies ( IFRC): It coordinates and gives international help to victims of natural and technological disasters, to refugees and in health emergencies.

International non-governmental agencies working for disaster management are:
a. International Rescue Committee (IRC): It provides lifesaving care and life-changing help to refugees forced to flee from war or disaster.

b. IMA World Health: It, in collaboration with USAID, the World Bank and many other organisations, builds sustainable health care systems.

c. CARE: It is an organisation fighting global poverty. It works for women and puts efforts to improve their basic education, prevent the spread of HIV by providing awareness among them, give them increase access to clean water and sanitation, expand economic opportunity for them. It provides emergency aid to survivors of war and natural disasters, and helps people rebuild their lives.

Indian organisations and institutes working for disaster management are:
a. National Disaster Response Force (NDRF): The multi-disciplinary, multi-skilled, high-tech force of the NDMA are capable of dealing with all types of natural and man-made disasters.

b. National Disaster Management Authority (NDMA): It lay down the policies, plans and guidelines for Disaster Management to ensure timely and effective response to disasters.

c. National Institute of Disaster Management (NIDM): It has been given the responsibilities for human resource development, capacity building, training, research, documentation and policy advocacy in the field of disaster management.

5. Make a survey of your school according to the plan of disaster management an write the pointwise information.

Question a.
Make a survey of your school according to the plan of disaster managment an write the pointwise information.
Answer:

This an activity based questions. Kindly do it yourself. But make sure to involve the following points in your survey:

• Primary information of the school: It should include information such as name and address of the school and Head Master, total number of school staff and name and phone numbers of school management members.
• School disaster management committee: Get the information of the members involved in disaster management committee.
• Detailed information about school building: Note the number of rooms, classroom, age of the building, types of roofs under this point.
• Information about school ground: It should include information like distance of ground from the main road, types of play grounds.
• Daily routine of the school: It should include information like working time of the school, lunch break time for the school.
• Possible hazards in the school: It should information such as record of past disaster happened in school, current planning for overcoming disasters.
• Disaster management map of the school: It should have information regarding all the buildings of the school, entrances and exit gates, place of probable danger, safer place at the time of disaster.

6. Are there any possible places of landslide in your area? Collect information from experts.

Question a.
Are there any possible places of landslide in your area? Collect information from experts.
Answer:
This is an activity based question. kindly do it yourself.

7. With the help of the following pictures, explain your role in disaster management.

Question a.
With the help of following pictures, explain your role in the disaster management.
Answer:

The picture given is not very clear. It does not indicate the condition of disaster. Therefore, there are two alternatives for this answer.
Option 1 : The boy holds a paper on which is written, ‘I am at risk’! The boy is shocked to read this. Someone has given message to him. He must search that person and help him or her. He should therefore take help from some elder or from police force in such matter.

Option 2 : The boy shown in the picture is in danger. So, he is typing in his I – pad, “I am at Risk”. After receiving this message, someone will help him. It depends upon, to whom is he sending this message. If he sends this message to us, we can immediately try to help him. His message “I am at Risk”, shows that he is in danger and has to be saved.
It is not clear about which disaster is shown in the picture.

Project:

Question 1.
Make a collection of news, photos. and cuttings about landslides and rift collapse.

Question 2.
With the help of Internet, collect information about the latest gadgets and technology to forecast earthquake.

Question 3.
Collect information about NDRF, RPF, CRPF, NCC from Internet.

Question 4.
Discuss- Need of CCTV.

Class 8 Science Chapter 9 Disaster Management Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
Earthquakes cause ……………. waves leading to movements of the earth’s surface.
Answer:
Earthquakes cause seismic waves leading to movements of the earth’s surface.

Question 2.
The central point of earthquake is the point above the ……………. on the earth’s surface.
Answer:
The central point of earthquake is the point above the epicentre on the earth’s surface.

Question 3.
The accentuation of earthquake is measured in …………… .
Answer:
The accentuation of earthquake is measured in ‘Richter Scale’.

Question 4.
If there is earthquake at the bottom of ocean, it may create ……………… waves.
Answer:
If there is earthquake at the bottom of ocean, it may create tsunami waves.

Question 5.
…………….. is the best device to put off small fires.
Answer:
Stirrup pump is the best device to put off small fires.

Question 6.
………………. of waterfalls occurs due to landslides.
Answer:
Displacement of waterfalls occurs due to landslides.

State whether the following statements are True or False:

Question 1.
Every year nearly 2,400 to 4,000 earthquakes occur on the earth.
Answer:
False. (Every year nearly 12,400 to 14,000 earthquakes occur on the earth.)

Question 2.
Potassium, sodium and calcium are the metals that react with water at high room temperature.
Answer:
False. (Potassium, sodium and calcium are the metals that react with water at normal room temperature.)

Question 3.
A fire caused due to electrical components is extinguished by fire extinguishers like carbon dioxide are used.
Answer:
True.

Question 4.
Indiscriminate cutting of the trees results in improvement of soil quality.
Answer:
False. (Indiscriminate cutting of the trees results in soil erosion.)

Question 5.
Landslide results in loss of plant life.
Answer:
True.

Match the column:

Question 1.

Answer:

Question 2.

Answer:

Name the following:

Question 1.
Modern equipment to get prior intimation about earthquake:
Answer:

1. Laser ranging
2. Very long baseline
3. Geiger counter
4. Creep meter
5. Strain meter
6. Tide gauge
7. Tilt meter
8. Volumetric strain gauge.

Question 2.
Some code of conduct made by Indian Standard Institute for construction of buildings:
Answer:

1. IS 456
2. IS 1893
3. IS 13920

Question 3.
The subcommittees of School Disaster Management.
Answer:

1. Fire extinguisher
2. Awareness
3. Instructions
4. Traffic management
5. Safety
6. Communication committee.

Answer the following questions in one sentence:

Question 1.
Which is the instrument or machine that records the intensity of earthquake?
Answer:
The machine/Instrument which records the earthquakes is called ‘Seismograph’ or ‘Seismometer’.

Question 2.
Which is the most common and effective solution for extinguishing fire ?
Answer:
Spraying water is the most common and effective solution for extinguishing fire.:

Question 3.
Which type of fires can be extinguished by the method of suppressing?
Answer:
To extinguish the fires caused due to electricity or oil, the method of suppressing the fire can be used.

Question 4.
Which metals react with water at normal room temperature?
Answer:
Combustible metals like potassium, sodium and calcium, react with water at normal room temperature.

Question 5.
Which metals react with water at higher temperatures?
Answer:
Magnesium, aluminum and zinc react with water at high temperatures.

Question 6.
Which institutes have launched a program to forecast the landslides and its effects?
Answer:
The Government of India in collaboration with Indian Mountaineering Institute and International Centre for Integrated Mountain Development has launched a program to forecast the landslides and its effects.

Give scientific reasons:

Question 1.
The electric mains are shut off immediately after the earthquake.
Answer:
There is increased possibility of short circuit after the earthquake. This may result in fire. The earthquake has already – brought the disaster. To prevent further destruction, the electric mains are shut off immediately after the earthquake.

Write short notes:

Question 1.
Types of fire:
Answer:
There are five types of fire. This division is based on two criteria, viz.
(i) Which substance is being burnt, (ii) What is the method of extinguishing it.
1. Class A Fire: Commonly inflammable solid things such as wood, clothes, coal, papers can be burnt by this type of fire. This fire is extinguished by spraying water over it. This is also called cooling out. Water is effectively used to put off class A fire.

2. Class B Fire: Flammable liquid substances such as petrol, oil, varnish, solvents, cooking oil, paints, etc. catch fire and it is called class B fire. Since these substances are lighter than water, they can be extinguished only by foaming fire extinguishers.

3. Class C Fire: The fire caused due to gaseous substances is called class C fire. Domestic gas (L.P.G.) and acetylene can cause such kind of fire.

4. Class D Fire: Combustible metals catch class D fire. Metals such as potassium, sodium and calcium, can react with water at normal room temperature whereas magnesium, aluminium and zinc react with water at high temperature. When both these groups combine with water, it causes explosion.

5. Class E Fire: When electric components are subjected to fire, they form class C fire. Such fires can be caused by short circuit or due to problems in electric fittings. Such fire is extinguished with the help of carbon dioxide and non-conductive fire extinguishers.

Question 2.
Disaster relief – planning.
Answer:
Anyone can face disaster at any time. The only way to tackle with such disasters is to keep preparedness to deal with any calamity. Schools, colleges and various offices need to chalk out a detailed planning in case of possible disasters. With this purpose in mind, disaster relief planning is done.

E.g. In the disaster relief planning for school, primary information of the school, the structure of School Disaster Management Committee, detailed information about school building and information about school ground, daily routine of the school such as at what time the school starts and what time does it end, the possible hazards in the school, and disaster management map of the school is included.

Answer the following questions:

Question 1.
What are the different ways to extinguish fire? Write briefly about them.
Answer:
There are three main methods to extinguish the fire. These methods are used to stop the spread of fire and to avoid the financial and other losses.
1. Cooling out by use of water: Water is easily available and can be used for putting off fire instantly. Due to spraying of water, there is cooling effect produced which helps in reducing the loss by fire. Fire can be easily controlled by water.

2. Suppressing the fire by covering it: When there is a fire due to electricity or oil it has to be controlled by covering the fire by sand or soil. When the froth is spread on the fire, there is no contact between air and fire. This puts off the fire and stops the spread of fire caused due to oil.

3. Keep away Flammable Substances: Care is taken to keep away all flammable substances from the fire. Wooden articles and inflammable substances are kept in such as way the fire will not engulf it. Stirrup pumps are used to put off small fires by which the water is spread in all directions around the fire.

Question 2
What are the safety measures and precautions to stop the fire?
Answer:

1. Switching off the regulator of cooking gas cylinder when not in use. Put off the connections of all electrical appliances when not in use.
2. If there is fire, call others immediately for help. Take help of others by calling them. Also help others who are in need to save their lives from fire.
3. Get help from fire brigade by calling phone number 101.
4. Know details about working of the fire extinguishing apparatus.
5. Give first aid to the victim of fire. Seek immediate medical help,

Question 3.
What are the causes of landslide?
Answer:

1. Various types of natural disasters like earthquakes, tsunami, heavy rains, storms, floods can result into landslide.
2. The indiscriminate cutting down of the trees can result into soil erosion. Soil erosion in turn results into landslide.
3. The construction of roads, bridges, railway tracks, etc. on the mountain slopes result into lot of digging. Such activities make soil cover loose. From the slopes the soil and rocks then can slide easily. This results into landslides.

Draw a well labelled diagrams:

Question 1
Seismometer/Secismograph.
Answer:

Question 2.
Focal point and epicenter or earthquake.
Answer:

Open-Ended Questions:

Question 1.
Have you at any time faced with any disaster? What were your experiences during such condition? How did you get rescued?
Answer:
Students should write their own experiences about such incidents if any.

Question 2.
In Maharashtra where do the traffic jams occur due to landslides? Make a list of such places. Why does the landslide occur at those places only? Discuss in the classroom and suggest preventive measures.
Answer:
In Maharashtra, the landslides are very common in the hilly regions. The traffic is suspended often during rainy season when such calamity strikes. Malshej, Khandala, Kasara are some of the Ghats which are very prone to land-slide. On the tracks of Konkan railway, the landslides are very common during heavy downpour.

The regions where more landslides occur have many constructions and large scale deforestation. The traffic of Konkan railway comes to standstill after such landslide. Moreover, during heavy monsoon days, the speed of the running trains is kept very slow. The soil structure is also responsible for such landslides.

Preventive measures: There should be wire meshing done across the sides of the roads and railway tracks so that the collapsed rocks and other debris does not obstruct the traffic. Tree plantation should be carried out to prevent loosening of the soil and rock. It will also help in preventing the soil erosion.

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 5 Inside the Atom Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 5 Inside the Atom

Class 8 Science Chapter 5 Inside the Atom Textbook Questions and Answers

1. Answer the following.

Question a.
What is the difference in the atomic models of Thomson and Rutherford?
Answer:

Question b.
What is meant by valency of an element? What is the relationship between the number of valence electron and valency?
Answer:
Valency: The capacity of an ; element to combine with another element is known as valency.
Valence electrons: The electrons in the outermost shell of an atom of an element are called valence electrons.
Helium and neon, atoms of both these gaseous element do not combine with any other atom. These elements are chemically inert, i.e. their valency is zero.

Helium atom contains two electrons, indicates that the outermost shell of helium has an electron duplet. The valence shell of neon is completely filled, i.e. neon has an electron octet. Similarly argon contains eight electrons in the valence shell, i.e. argon has an electron octet. It is confirmed that the valency is zero when electron octet (or duplet) is complete.

Atoms of all the elements except inert gases have tendency to combine with other atoms, i.e. they have a non zero valency. The molecules formed by combination with hydrogen (E.g. H₂, HCl) that valency of hydrogen is one. The electronic configuration of hydrogen shows that there is one electron less than the complete duplet state. This number ‘one’ matches with the valency of hydrogen which is also one.

It means that there is relationship between the valency of an element and the number of electrons in its valence shell.

Question c.
What is meant by atomic mass i number? Explain how the atomic number and mass number of carbon are 6 and 12 respectively.
Answer:
The total number of protons and neutrons in the nucleus of the atom is called the atomic mass number. The atomic number, i.e. the proton number of carbon is 6 and the mass number is total number of protons and neutrons in the carbon, i.e. 6 protons + 6 neutrons = 12. Therefore, the atomic number and mass number of carbon are 6 and 12 respectively.

Question d.
What is meant by subatomic particle? Give brief information of three subatomic particles with reference to electrical charge, mass and location.
Answer:
A particle which is a constituent of an atom hence smaller than the atom is called subatomic particle.
An atom is formed from the nucleus and the extranuclear part. These contain three types of subatomic particles.
The nucleus contains two types of subatomic particles together called nucleons. Protons and neutrons are the two types of nucleons or subatomic particles and electrons are subatomic particles in the extra nuclear part.

1. Proton (p): Proton is a positively charged subatomic particle in the atomic nucleus. The positive charge on the nucleus is due to the proton in it. A proton is represented by the symbol ‘p’. Each proton carries a positive charge of +1e. (1e = 1.6 × 10^-19 coulomb). When total positive charge on the nucleus is expressed in the unit ‘e’, its magnitude is equal to the number of proton in the nucleus.
The mass of one proton is approximately lu (1 Dalton).
(1u = 1.66 × 10^-27g) (The mass of one hydrogen atom is also approximately lu.)

2. Neutron (n): Neutron is an electrically neutral subatomic particle and is denoted by the symbol ‘n’. The number of neutron in the nucleus is denoted by the symbol ‘N’ Atomic nuclei of all the elements except hydrogen with atomic mass lu, contain neutrons. The mass of a neutron is approximately lu, which is almost equal to that of a proton.

3. Electron (e^–): Electron is a negatively charged subatomic particle and is denoted by the symbol ‘e-’. Each electron carries one unit of negative charge (-1e). Mass of an electron is 1800 times less than that of a hydrogen atom. Therefore the mass of an electron can be treated as negligible. Electron in the extranuclear part revolve in the discrete orbits around the nucleus. The energy of an electron is determined by the shell in which it is present.

2. Give scientific reasons:

Question a.
All the mass of an atom is concentrated in the nucleus.
Answer:

1. The nucleus of an atom contains protons and neutrons.
2. The electrons revolve around the nucleus.
3. The mass of an electron is negligible compared to that of a proton or a neutron.
4. Hence, the mass of an atom depends mainly on the number of protons and neutrons. Therefore, practically all the mass of an atom is concentrated in the nucleus.

Question b.
Atom is electrically neutral.
Answer:

1. An atom is made of two parts, viz. the nucleus and the extranuclear part.
2. The nucleus is positively charged. The positive charge on the nucleus is due to protons.
3. The extranuclear part of an atom is made of negatively charged electrons.
4. In an atom, the number of protons is equal to the number of extranuclear electrons.
5. The magnitude of the positive charge on the nucleus equals the magnitude of the negative charge on the electrons. As the opposite charges are balanced, the atom is electrically neutral.

Question c.
Atomic mass number is a whole number.
Answer:

1. The total number of protons and neutrons in the nucleus of the atom is called the atomic mass number (A).
2. As protons and neutrons are whole numbers, the atomic mass number is also a whole number.

Question d.
Atoms are stable though negatively charged electron are revolving within it.
Answer:

1. The entire mass of the atom is concentrated in the nucleus and the positively charged nucleus at centre of an atom.
2. The negatively charged electrons revolve around the nucleus.
3. The total negative charge on all the electron is equal to positive charge on the nucleus. As the opposite charges are balanced, the atom is stable.

3. Define the following terms.

Question a.
Atom:
Answer:
An atom is the smallest particle of an element which retains its chemical identity in all physical and chemical changes.

Question b.
Isotope
Answer:
Atoms of the same element having the same atomic number, but different atomic mass numbers are called isotopes.

Question c.
Atomic number
Answer:
The number of electrons or protons in an atom is called the atomic number. It is denoted by Z.

Question d.
Atomic mass number
Answer:
The total number of protons and neutrons in the nucleus of the atom is called the atomic mass number. It is denoted by A.

Question e.
Moderator in nuclear reactor
Answer:
The substance which reduces the speed of fast-moving neutrons produced in a fission is called a moderator.

4. Draw a neal labelled diagram.

Question a.
Explain Rutherford’s scattering experiment.
Answer:

Alpha particles emitted by radioactive element bear a positive charge. Rutherford bombarded alpha particles through a very thin gold foil. He observed the path of α – particles by means of a fluorescent screen around the gold foil. It was expected that

1. Most of the alpha particles passed through the gold foil without any deviation.
2. Some alpha particles were deflected from their path through small angles.
3. A few alpha particles were scattered at large angles.
4. A still smaller number of same sign particles get deflected through a larger angle and one a-particle out of 20000 bounced back in the direction opposite to the original path.

Question b.
Thomson’s atomic model.
Answer:
Thomson’s plum pudding model of atom:

1. According to Thomson’s model the positive charge is distributed throughout the atom and the negatively charged electron: are embedded in a gel of positive charge (a plum pudding model).
2. The distributed positive charge is balanced by the negative charge on the electrons. Therefore the atom becomes electrically neutral.

Question c.
Diagrammatic sketch of electronic configuration of magnesium (Atomic number 12).
Answer:

Question d.
Diagrammatic sketch of electronic configuration of argon (Atomic number 18).
Answer:

5. Fill in the blanks.

Question 1.
Electron, proton, neutron are the types of ………… in an atom.
Answer:
Electron, proton, neutron are the types of subatomic particles in an atom.

Question 2.
An electron carries a ……………. charge.
Answer:
An electron carries a negative charge.

Question 3.
The electron shell ………….. is nearest to the nucleus.
Answer:
The electron shell K is nearest to the nucleus.

Question 4.
The electronic configuration of magnesium is 2, 8, 2. From this it is understood that the valence shell of Magnesium is …………….. .
Answer:
The electronic configuration of magnesium is 2, 8, 2. From this it is understood that the valence shell of Magnesium is M.

Question 5.
The valency of hydrogen is one as per the molecular formula H₂O. Therefore valency of ‘Fe’ turns out to be ………….. as per the formula Fe₂O₃.
Answer:
The valency of hydrogen is ‘one’ as per the molecular formula H₂O. Therefore valency of ‘Fe’ turns out to be 3 as per the formula Fe₂O₃.

6. Match the pairs.

Question 1.

Answer:

7. Deduce from the datum provided.

Question 1.

Answer:
1. There are 12 neutrons in the sodium \(\left({ }_{11}^{23} \mathrm{Na}\right)\).
(N = A – Z) 23 – 11 = 12
2. Atomic mass number of \({ }_{6}^{14} \mathrm{C}\) is 14.
3. There are 17 protons in chlorine \(\left({ }_{37}^{17} \mathrm{Cl}\right)\)

Project:

Explain the atomic models using the material such as old C.D., balloon, thread, marbles, etc.

Class 8 Science Chapter 5 Inside the Atom Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
An atom is electrically ……………. .
Answer:
An atom is electrically neutral.

Question 2.
Except hydrogen, the nuclei of all atoms contain ………….. .
Answer:
Except hydrogen, the nuclei of all atoms contain neutrons.

Question 3.
\({ }_{6}^{12} \mathrm{C}\), …………… and …………. are isotopes of carbon.
Answer:
\({ }_{6}^{12} \mathrm{C}\), \({ }_{6}^{13} \mathrm{C}\) and \({ }_{6}^{14} \mathrm{C}\) are isotopes of carbon.

Question 4.
An atom has 11 protons and …………. neutrons and hence its atomic mass number is 23.
Answer:
An atom has 11 protons and 12 neutrons and hence its atomic mass number is 23.

Question 5.
The element ………….. has two electrons in the K shell, but it is a noble gas.
Answer:
The element helium has two electrons in the K shell, but it is a noble gas.

Question 6.
Isotopes of the element have the same ……….. properties.
Answer:
Isotopes of the element have the same chemical properties.

Question 7.
Electrons must absorb …………….. to transit between orbits.
Answer:
Electrons must absorb energy to transit between orbits.

Question 8.
……….. discovered the electron.
Answer:
J. J. Thomson discovered the electron.

Question 9.
∝ – particles have ………….. charge.
Answer:
∝ – particles have positive charge.

Question 10.
Electrons revolve around the …………….. in certain discrete orbits.
Answer:
Electrons revolve around the nucleus in certain discrete orbits.

Question 11.
The shell-wise distribution of electrons is called the ………………… .
Answer:
The shell-wise distribution of electrons is called the electronic configuration.

Question 12.
Democritus termed the smallest particles of matter as …………… .
Answer:
Democritus termed the smallest particles of matter as atoms.

Question 13.
………………. discovered neutron.
Answer:
James Chadwick discovered neutron.

Question 14.
Electrons revolve around the nucleus in paths called ………….. .
Answer:
Electrons revolve around the nucleus in paths called orbits.

Question 15.
The second shell has the capacity of ……………… .
Answer:
The second shell has the capacity of 8 electrons.

Question 16.
Electrons in the ………….. shell have minimum energy.
Answer:
Electrons in the K or first shell have minimum energy.

Question 17.
Electrons in an atom occupy shells in increasing order of …………… .
Answer:
Electrons in an atom occupy shells in increasing order of energy.

Question 18.
Atomic masses are measured in a unit called …………… .
Answer:
Atomic masses are measured in a unit called dalton.

Question 19.
According to the atomic model of …………….., electrons are embedded in a gel of positive charge.
Answer:
According to the atomic model of Thomson, electrons are embedded in a gel of positive charge.

Question 20.
All atoms, except ………….. contain neutrons in their nuclei.
Answer:
All atoms, except normal hydrogen contain neutrons in their nuclei.

Question 21.
The maximum capacity of the M shell is ………………… electrons.
Answer:
The maximum capacity of the M shell is 18 electrons.

Question 22.
The atom of the element ……………. has eight electrons in the outermost shell.
Answer:
The atom of the element neon has eight electrons in the outermost shell.

Rewrite the following statements selecting the correct options:

Question 1.
The symbol A is used to denote the …………. .
(a) atomic number
(b) atomic radius
(c) atomic mass number
(d) atomic mass
Answer:
(c) atomic mass number

Question 2.
The existence of isotopes is due to the presence of different number of …………….. .
(a) electrons
(b) protons
(c) neutrons
(d) positrons
Answer:
(c) neutrons

Question 3.
In the nucleus of a sodium atom (\({ }_{11}^{23} \mathrm{Na}\)), there are ……………… neutrons.
(a) 11
(b) 12
(c) 10
(d) 9
Answer:
(b) 12

Question 4.
Isotopes of an element have the same number of …………….. .
(a) neutrons
(b) nucleons
(c) electrons
(d) atoms
Answer:
(c) electrons

Question 5.
The great Indian philosopher ………….. proposed that matter is made up of invisible tiny particles.
(a) Aryabhatta
(b) Kanad
(c) Bhaskaracharya
(d) Chanakya
Answer:
(b) Kanad

Question 6.
The maximum capacity of the M shell is …………… electrons.
(a) 2
(b) 8
(c) 18
(d) 32
Answer:
(c) 18

Question 7.
The mass of the electron is …………….. times less than that of a hydrogen atom.
(a) 1800
(b) 8100
(c) 1550
(d) 1600
Answer:
(a) 1800

Question 8.
The L shell is the valence shell in …………. .
(a) hydrogen
(b) chlorine
(c) oxygen
(d) sodium
Answer:
(c) oxygen

Question 9.
The M shell is the valence shell in ……………….. .
(a) fluorine
(b) neon
(c) carbon
(d) chlorine
Answer:
(d) chlorine

Question 10.
The N shell is the valence shell in ………….. .
(a) fluorine
(b) chlorine
(c) bromine
(d) helium
Answer:
(c) bromine

Question 11.
The maximum capacity of the N shell is ……………. electrons.
(a) 2
(b) 32
(c) 18
(d) 8
Answer:
(b) 32

Question 12.
The maximum number of electrons that can be accommodated in the third orbit is ………… .
(a) 3
(b) 8
(c) 32
(d) 18
Answer:
(d) 18

Question 13.
Rutherford alpha-particle scattering experiment was responsible for the discovery of the ………………. .
(a) atomic nucleus
(b) proton
(c) electron
(d) atomic mass
Answer:
(d) atomic mass

Question 14.
Isotopes of element have …………….. .
(a) different atomic numbers and different atomic mass
(b) different atomic numbers but the same atomic mass number
(c) the same atomic number but different atomic mass numbers
(d) the same atomic number and the same atomic mass number
Answer:
(c) the same atomic number but different atomic mass numbers

Question 15.
The nucleus of an atom contains 19 protons and 21 neutrons. The atomic mass number of the element is ………….. .
(a) 19
(b) 21
(c) 40
(d) 39
Answer:
(c) 40

Question 16.
The nucleus of an atom contains 18 protons and 22 neutrons. The atomic number of the element is ……………… .
(a) 18
(b) 40
(c) 22
(d) 4
Answer:
(a) 18

Question 17.
When writing the symbol of its …………… and ………….. are written.
(a) atomic number, atomic mass number
(b) protons, electrons
(c) protons, neutrons
(d) atomic number, electrons
Answer:
(a) atomic number, atomic mass number

Question 18.
The particles in the atomic nucleus are …………….. .
(a) protons and electrons
(b) electrons
(c) electrons and neutrons
(d) protons and neutrons
Answer:
(d) protons and neutrons

State whether the following statements are True or False:

Question 1.
An atom as a whole is electrically neutral
Answer:
True.

Question 2.
The mass of an atom is distributed evenly within it.
Answer:
False. (The mass of atom is not distributed evenly, practically all the mass is concentrated in the nucleus.)

Question 3.
The electron has the same mass as that of the proton.
Answer:
False. (The mass of the electron is much less than that of the proton.)

Question 4.
The electron in the K shell has maximum energy.
Answer:
False. (The electrons in the K shell has minimum energy.)

Question 5.
Isotopes have same atomic number but different atomic mass number.
Answer:
True.

Question 6.
Matter is composed of molecules and molecules are made of atoms.
Answer:
True.

Question 7.
In India, total 22 nuclear reactors in eight places are functioning.
Answer:
True.

Question 8.
The number of electrons in a given orbit is given by the formula n
Answer:
False. (The number of electrons in a given orbit is given by the formula 2n2)

Question 9.
Atomic masses are measured in a unit called the dalton (u).
Answer:
True.

Question 10.
The chemical properties of isotopes are different.
Answer:
False. (The chemical properties of isotopes are the same.)

Question 11.
The maximum capacity of the N shell is 18 electrons.
Answer:
False. (The maximum capacity of the N shell is 32 electrons.)

Question 12.
Deuterium is an isotope of hydrogen.
Answer:
True.

Question 13.
Isotopes are used in the treatment of cancer.
Answer:
True.

Question 14.
Atoms of all elements, except normal hydrogen contain neutrons.
Answer:
True.

Question 15.
Electrons moving in different orbits possess the same amount of energy.
Answer:
False. (Electrons moving in different orbits possess different amounts of energy.

Question 16.
Rutherford discovered the neutron.
Answer:
False. (Chadwick discovered the neutron.)

Question 17.
The nth orbit contains at the most 2n² electrons.
Answer:
True.

Question 18.
Electrons have different energies according to their orbits.
Answer:
True.

Question 19.
The capacity of the second orbit is 18 electrons.
Answer:
False. (The capacity of the second orbit is 8 electrons.)

Question 20.
The radioactive isotope Sodium-24 is used in the medical treatment of cancer.
Answer:
False. (The radioactive isotope Sodium-24 is used for detection of cracks in the underground pipes.)

Question 21.
Uranium-235 is used in the production of electricity.
Answer:
True.

Consider the relation between I the items in the first pair and write the correlation for second pair:

Question 1.
K : 2 : M : …………. .
Answer:
18

Question 2.
Carbon : 2, 4 : : Fluorine : …………….. .
Answer:
2, 7

Question 3.
Nitrogen : Valency three : : Fluorine : …………….. .
Answer:
valency one

Question 4.
Atomic radius : pm : Atomic mass : ……………. .
Answer:
u

Question 5.
NaH : Valency of Na : 1 : : MgCl₂ : Valency of Mg …………… .
Answer:
2

Question 6.
\(35 \mathrm{Cl}\) : number of neutrons 18 : : \({ }^{37} \mathrm{Cl}/latex] : …………….. .
Answer:
number of neutrons 20

Question 7.
Protons : Positive : : ……………. : Neutral.
Answer:
Neutrons.

Match the following:

Question 1.

Answer:

Question 2.

Answer:

Question 3.

Answer:

Distinguish between the following:

Question 1.
Proton and Neutron:
Answer:

Question 2.
Neutron and Electron:
Answer:

Question 3.
Proton and Electron:
Answer:

Question 4.
Atomic number and Atomic mass number:
Answer:

Answer the following questions in one sentence each:

Question 1.
Name the particles which are present in the nucleus of an atom.
Answer:
Protons and neutrons are present in the nucleus of an atom.

Question 2.
State the relation between the number of protons, the number of neutrons and the atomic mass number (A) of an element.
Answer:
Atomic mass = Number of + Number of number (A) protons (p) neutrons (n)

Question 3.
Chlorine contains 17 protons and 18 neutrons. What is its atomic mass number?
Answer:
The atomic mass number of chlorine is 35.

Question 4.
Carbon contains 6 protons and 6 neutrons. State its atomic number and atomic mass number.
Answer:
The atomic number of carbon is 6 and the atomic mass number is 12.

Question 5.
State one use of isotopes of cobalt.
Answer:
Isotopes of Cobalt-60 are used in the treatment of cancer.

Question 6.
State one use of isotopes of i uranium.
Answer:
Isotopes of uranium are used for production of electrical energy.

Question 7.
Write the electronic configuration of oxygen.
Answer:
Electronic configuration of oxygen is 2, 6.

Question 8.
Write the electronic configuration of chlorine.
Answer:
Electronic configuration of chlorine is 2, 8, 7.

Question 9.
State the number of electrons in the L shell of lithium.
Answer:
There is one electron in the L shell of lithium.

Question 10.
State the number of electrons in the M shell of argon.
Answer:
There are 8 electrons in the M shell of argon.

Question 11.
State the number of electrons in the K shell of helium.
Answer:
There are two electrons in the K shell of helium.

Question 12.
Name isotopes of hydrogen.
Answer:
Hydrogen, Deuterium and Tritium are the isotopes of hydrogen.

Question 13.
Name two isotopes of carbon.
Answer:
[latex]{ }_{6}^{12} \mathrm{C}\) and \({ }_{6}^{14} \mathrm{C}\) are the isotopes of carbon.

Question 14.
Name two elements in which the K and L shells of an atom are completely filled with electrons.
Answer:
The elements are neon and argon.

Question 15.
From the symbol \({ }_{8}^{16} \mathrm{O}\), state the electronic configuration of oxygen and the atomic mass number of isotope oxygen.
Answer:
Electronic configuration of oxygen : 2, 6. Atomic mass number of oxygen : 16.

Question 16.
The atomic mass number of an element is 18, and the element contains 8 electrons. What is the number of protons and neutrons in it?
Answer:
Number of protons : 8, Number of neutrons : 10.

Question 17.
An atom contains 2 protons, 2 electrons and 3 neutrons. State its atomic number and atomic mass number.
Answer:
Atomic number: 2, Atomic mass number: 5.

Question 18.
How many electrons could there be in the outermost orbit of an element whose valency is 3?
Answer:
If the valency of an element is 3 then there is a possibility of 3 or 5 electrons in the outermost orbit.

Question 19.
Which element is used as fuel in atomic reactors?
Answer:
Isotopes of uranium are used as fuel in atomic reactors.

Question 20.
Name the place and the first nuclear reactor in India.
Answer:
Apsara at Bhabha Atomic Research Centre in Mumbai is the first nuclear reactor in India.

Answer the following questions:

Question 1.
Explain Dalton’s atomic theory.
OR
Write the postulates of Dalton’s atomic theory.
Answer:
Dalton’s atomic theory:

1. According to Dalton’s atomic theory matter is made up of atoms and atoms are indivisible and indestructible.
2. All atoms of an element are alike while different element have different atom with different mass.

Try this:

Question a.
Take a solid ball and a Bundi Laddu. Press both these spheres with your palms. What did you find?
Answer:
Solid ball does not break and Bundi Laddu breaks into pieces if you press hard.

Question b.
Cut the solid ball with a sharp knife. What did you find?
Answer:
There is no cavity inside the ball.

Question 2.
How will you think about atomic mass distribution according to Thomson’s I model? Whether this distribution is uniform or non uniform as per Dalton’s atomic theory?
(Use your brainpower!
Answer:
In Thomson’s model the distribution of atomic mass is uniform. Dalton’s atomic theory does not say anything about atomic mass distribution.

Question 3.
If the striker flicked by you misses the coin that you aimed at, where would the striker go?
Can you tell?
Answer:
The striker will continue to move practically with the same velocity till it strikes some other coin or the edge of the board or enter the pocket.

Question 4.
If the striker hits the coin, in which direction would it go? Straight forward to a side or in the reverse direction?
Answer:
Striker may go straight forward or it may be deflected depending upon the exact direction of the motion of the striker.

Question 5.
Draw a neat labelled diagram of Thomson’s atomic model.
Answer:

Question 6.
What were the conclusions drawn from the alpha particle experiment performed hy Rutherford?
Answer:
On the basis of the alpha particle experiment the following conclusions were drawn by Rutherford:

1. An atom has tiny, dense positively charged nucleus at centre of an atom.
2. Most of the mass of the atom is concentrated in the nucleus.
3. Negatively charged particles called electrons revolve around the nucleus.
4. The total negative charge on all the ; electron is equal to the positive charge on ‘ the nucleus. As the opposite charges are balanced, the atom is electrically neutral.
5. There is an empty space between the i revolving electron and the atomic nucleus.

Question 7.
Explain Rutherford’s atomic model.
Answer:

1. An atom has tiny, dense, positively charged core called the nucleus.
   
2. Most of the mass of the atom is concentrated in the nucleus.
3. Electrons bear negative charge. They revolve around the nucleus in orbits.
4. The structure of an atom may be regarded as a miniature of the solar system, the nucleus as the sun and the electrons as the planets.

Question 8.
Which discovery did point out that an atom has internal structure?
(Use your brainpower!
Answer:
The discovery of radioactivity (1896) pointed out that an atom has internal structure.

Question 9.
What is the difference between the solid atom in Dalton’s atomic theory and Thomson’s atomic model?
(Use your brain power!
Answer:
The solid atom in Dalton’s atomic theory is a single particle it does not have any structure and also does not have any constituents. In Thomson’s model, atom is made of positive and negative charges. Thus it is not a single particle. It has constituents and has internal structure.

Question 10.
Explain the difference between the distribution of positive charge in Thomson’s atomic model and Rutherford’s atomic model.
(Use your brain power!
Answer:
According to Thomson’s atomic model, the atom is a homogeneous sphere of positive charge. According to Rutherford’s atomic model, the positive charge is concentrated in the nucleus.

Question 11.
What is the point difference between the place of electron in the atomic models of Thomson and Rutherford?
(Use your brain power!
Answer:
According to Thomson’s atomic model, the negatively charged electrons are embedded in a gel of positive charge and they are stationary. According to Rutherford’s atomic model, the negatively charged electrons revolve around the nucleus.

Question 12.
What is the thing which is present in Rutherford’s atomic model and not present in Dalton’s and Thomson’s atomic models?
(Use your brain power!
Answer:
1. Dalton’s atomic model:
Dalton’s atomic theory does not tell anything about the structure of the atom. There is no mention of electron in Dalton’s atomic theory.

Rutherford’s atomic model:
Rutherford’s atomic model tells about the structure of the atom, i.e. the electron revolving around the nucleus.

2. Thomson’s atomic model:
The electrons are embedded in a gel of positive charge. Here the electrons are stationary and there is no concept of nucleus.

Rutherford’s atomic model:
In Rutherford’s atomic model, the electrons are not stationary, they revolve around the nucleus which is positively charged.

Question 13.
Explain Niels Rohr’s atomic model.
OR
Write the postulates of Bohr’s atomic model.
Answer:
The important postulates of Bohr’s atomic model are as follows:

1. The electrons revolving around the atomic nucleus lie in the concentric circular orbits at certain distance from the nucleus.
2. Energy of an electron is constant while it is in a particular orbit.
3. When an electron jumps from an inner orbit to an outer orbit it absorbs specific amount of energy, and when it jumps from an outer orbit to an inner orbit it emits specific amount of energy.
4. The energy emitted or absorbed during these transitions is equal to energy difference between the initial state and the final state of the electron.

Question 14.
How many types of subatomic particles are found in atom?
Use your brainpower!
Answer:
There are three types of subatomic particles found in atom, viz. the proton, neutron and electron.

Question 15.
Which subatomic particles are electrically charged?
Use your brain power!
Answer:
The proton is a positively charged subatomic particle and the electron is a negatively charged particle.

Question 16.
Which subatomic particles are present in the nucleus?
Use your brain power!
Answer:
The proton and neutron are present in the nucleus.

Question 17.
Where are electrons revolving around the nucleus placed?
Use your brain power!
Answer:
Electrons revolve in the discrete orbits around the nucleus.

Question 18.
State the characteristics of the neutron.
Answer:

1. The neutron is electrically neutral and is denoted by the symbol ‘N’.
2. It is present in the nucleus along with the proton.
3. The mass of the neutron is almost equal to lu which is almost equal to that of the proton.

Question 19.
State the characteristics of protons.
Answer:

1. Protons are positively charged particles and are denoted by the symbol ‘P’.
2. They are present in the nucleus of an atom.
3. The mass of the proton is very nearly equal to lu which is almost equal to that of the hydrogen atom.
4. All the elements contain protons.

Question 20.
State the characteristics of electrons.
Answer:

1. Electrons are negatively charged particles and are denoted by the symbol ‘e’.
2. They have negligible mass.
3. They revolve around the nucleus in certain discrete orbits.
4. In an atom, the number of electrons is equal to the number of protons in its nucleus (Z).

Question 21.
The symbol used for oxygen is ‘O’. There are 8 protons and 8 neutrons in its nucleus. From this determine the 1 atomic number (Z) and mass number (A) of oxygen and arrange these in a 1 conventional symbol.
Use your brain power!
Answer:
Atomic mass number
= Protons + Neutrons
= 8 + 8
Atomic mass number = 16
Atomic number, i.e. the proton number = 8
The conventional symbol = \(\mathrm{A} \mathrm{O}\)
Z = Atomic number
i.e. number of protons is 8.
A = Atomic mass number = 16.
The conventional symbol = \({ }_{8}^{16} \mathrm{O}\).

Question 22.
Atomic number of carbon is 6. How many electrons are there in a carbon atom?
Use your brainpower!
Answer:
The atomic number of carbon, i.e. the proton number of carbon is 6.
The number of electron in the extranuclear part is equal to the number of protons in the nucleus.
∴ The number of electrons in a carbon atom = 6.

Question 23.
A sodium atom contains 11 electrons. What is the atomic number of sodium?
Use your brain power!
Answer:
The number of electron in the extranuclear part is equal to the number of protons, i.e. atomic number. The atomic number of sodium is 11.

Question 24.
The atomic number and mass number of magnesium are 12 and 24 respectively. How will you show this by the convention symbol?
Use your brainpower!
Answer:
The atomic number, atomic mass number and the symbol of an element are written as:

\({ }_{12}^{24} \mathrm{Mg}\) the conventional symbol for magnesium.

Question 25.
The atomic number and mass number of calcium are 20 and 40 respectively. Deduce the number of neutron present in the calcium nucleus.
Use your brain power!
Answer:
There are 20 neutrons in the nucleus of calcium.
[Note: The number of neutrons N = A – Z = 40 – 20 = 20]

Question 26.
Write a note on distribution of electrons in orbits.
OR
What is the maximum number of ( electrons that can be accommodated in each of the orbits (shells) K, L, M, N, etc.?
Answer:
The number of maximum electrons in different orbits of the atom are fixed. The orbit (shell) closest to the nucleus is: given the number 1, the next orbit the ; number 2… etc. The orbits one are designated ; by letters K, L, M, N,… corresponding to the shell numbers n = 1, 2, 3, 4, … etc. The maximum number of electrons in a given orbit is 2n², when n is the number of orbit (shell), thus the first shell has the capacity of 2 electrons, the second 8, the third 18, the fourth 32 and so on. The electrons in the K shell have minimum energy. The electrons in the subsequent shells possess higher energy.

Question 27
There is a similarity in atomic structure and solar system. The planets revolve around the sun due to the gravitational force. Which force might be acting in the atomic structure?
Can you tell?
Answer:
The electric force might be acting in the atomic structure. In the atomic structure, electric force is much stronger than gravitational force.
[Note: Here the gravitational force is very very small compared to the electric force, therefore, the gravitational force can be ignored.]

Question 28.
Positively charged proton are together in the nucleus. What might be, one of the function of the neutrons in the nucleus?
Can you tell?
Answer:
One of the function of the neutrons in the nucleus is to keep the protons and neutrons together by nuclear force.

Question 29.
What do you understand by electronic configuration?
Answer:
The shellwise distribution of the electron in an atom of an element is called the electronic configuration.?

Question 30.
Write the electronic configuration of the following elements:
(1) Hydrogen, (2) Magnesium. (3) Aluminium, (4) Phosphorus, (5) Sulphur.
Answer:

Question 31.
Use the following molecular formulae to determine the valencies of H, Cl, O, S, N, C, Br, I, Na.
Molecular formulae – H₂, HCl, H₂O, H₂S, NH₃, CH₄, HBr, HI, NaH.
Can you recall?
Answer:

Question 32.
Draw suitable diagrams to show the electronic configuration of the atoms of the following elements: Hydrogen, helium, carbon, neon, sodium, chlorine.
Answer:

Question 33.
What are the symbols used for the shells which accommodate the electrons in various atoms?
Use your brain power!
Answer:
The symbols used for the shells which accommodate the electrons are K, L, M, N, … respectively.

Question 34
What is the symbol and ordinal number of the innermost shell?
(Use your brain power!
Answer:
The symbol of the innermost shell is K and ordinal number of the innermost shell is 1.

Question 35.
Write symbol of electron distribution in shell of fluorine atom?
Use your brain power!
Answer:
Symbol for fluorine atom = F,
Electronic configuration of fluorine \(\begin{array}{l}\mathrm{K} \\2\end{array}\), \(\begin{array}{l}\mathrm{L} \\7\end{array}\).

Question 36.
Which is the outermost shell of fluorine atom?
Use your brain power!
Answer:
The outermost shell of fluorine atom is L.

Question 37.
Which is the outermost shell of sodium atom?
Use your brain power!
Answer:
The outermost shell of sodium atom is M shell.

Question 38.
Which is the outermost shell of hydrogen atom?
Use your brain power!
Answer:
The outermost shell of hydrogen is K shell.

Question 39.
What is meant by the atomic number (Z) of an element?
(Use your brain power!
Answer:
Atomic number (Z): The number of electrons or protons in an atom is called the atomic number. It is denoted by Z.

Question 40.
Atomic numbers (Z) of some elements are given here. Write down the number of electron present in the outermost shell of each of them.
Use your brain power!
Answer:

Question 41.
The number of electrons of some elements is given here. By using it write the electronic configuration, number of valence electron and valency of the respective elements.
Use your brain power!
Answer:

Question 42.
Why are the atomic numbers and atomic mass numbers always in whole numbers?
Use your brain power!
Answer:
The total number of protons and neutrons in the nucleus of the atom is called the atomic mass number (A). The number of electrons or protons in an atom is called the atomic number (Z). Both protons and neutrons are whole numbers, therefore, atomic numbers and atomic mass numbers are always in whole numbers.

Question 43.
Sulphur contains 16 protons and 16 neutrons. What would be its atomic number and mass number?
Use your brain power.
Answer:
The atomic number of sulphur is 16 and the atomic mass number is 32.

Question 44.
State the uses of isotopes.
Answer:
Isotopes of some elements are radioactive. Isotopes are used in various fields such as industry, agriculture, medicine, research field.

1. Isotopes of uranium is used for nuclear fission and production of electricity.
2. Cobalt – 60 are used in the treatment of cancer.
3. Iodine – 131 is used in the treatment of goitre.
4. The radioactive isotopes, Sodium – 24 are used for detection of cracks (leakage) in the underground pipes.
5. Radioactive isotopes are used for food preservation from microbes.
6. The radioactive C – 14 is used for determining the age of archaeological objects.

Question 45.
Write a note on nuclear reactor.
Answer:
1. A machine that generates electricity on large scale by using atomic energy is called a nuclear reactor. In a nuclear reactor, the nuclear energy in atom is released by bringing about nuclear reactions on the nuclear fuel.

2. When uranium – 235 is bombarded with a slow speed neutron, it undergoes nuclear fission. Various elements are produced. For example: Krypton – 92 and Barium – 141 along with 2 to 3 neutrons are emitted on fission, these neutron have high speed. Their speed is reduced and they are used for bombarding more Uranium – 235 nuclei.

The process is repeated many times. In this way a chain reaction of nuclear fission takes place (See the figure). A large amount of nuclear energy is released during a chain reaction of fission. The chain reaction is controlled to prevent the probable explosion.

Neutrons are slowed down using graphite or heavy water as moderator. The chain reaction is controlled by absorbing neutron with the help of rods of boron, cadmium and beryllium. The heat produced in the fission is taken out by water as coolent. Water is converted into steam. The available heat is used to drive turbines to produce electricity.

Give scientific reasons:

Question 1.
In Rutherford’s experiment, some alpha particles colliding with the thin gold foil are turned back.
Answer:
1. All the positive charges in an atom is concentrated in a very small region at the centre of the atom. This region is called the nucleus. Electrons revolve around the nucleus, but most of the atom is empty. Alpha particles are positively charged.

2. When a thin sheet of gold is bombarded by alpha particles, most of the particles pass through it without deviation as the atom is almost empty. But some alpha particles move directly towards the positive nuclei, collide with them and due to the electric repulsion, turn back. Thus, in Rutherford’s experiment, some alpha particles colliding with the thin gold foil are turned back.

Question 2.
Two electrons in helium atom are placed in only one shell while three electrons in lithium atom occupy two shells.
Answer:
1. The electronic configuration of helium is (2). It indicates that helium atom has two electrons. Both the electrons are accommodated in the K shell. The maximum capacity of the K shell is two electrons and is maintained in all the elements. Hence, two electrons in helium are placed in only one shell.

2. The electronic configuration of lithium is (2, 1). It indicates that lithium atom has three electrons. The first shell K accommodates two electrons, i.e., the maximum capacity of the K shell. The remaining electron is accommodated in the next shell, i.e., the L shell. Thus, three electrons in lithium occupy two shells (K and L).

Complete the following:

Question 1.
Complete the table by putting tick mark in appropriate box.
Answer:
Types of substances:

Question 2.
Complete the table:
Answer:

Write the maximum number of electron in a shell using the above table. K Shell : 2, L Shell : 8, M Shell : 18, N Shell : 32.

Question 3.
Complete the table:
Answer:
Electronic configuration of some elements:

Question 4.
Complete the following table:
Answer:
Relationship between valency and electronic configuration:

Question 5.
In table 4 column you have written of that element? How many electrons identified valency from its molecular are used to complete the octet? formulae. When the number of the valency electrons in an element ‘x’ is 4 or less than 4, does ‘x’ match with the valency of that element?
Use your brain power!
Answer:
When the number of the valence electrons in an element x is 4 or less than 4, then x matches with the valency of that element.

Question 6.
When the number of the valence electrons in an element ‘x’ is 4 or more than 4, does’(8 – x)’ match with the valency of that element? How many electrons are used to complete the octet?
(Use your brain power!
Answer:
When the number of the valence electrons in an element x is 4 or more than 4, then (8-x) matches with the valency of that element. (8-x) electrons are used to complete the octet.

Question 7
Complete the table:
Answer:

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 4 Current Electricity and Magnetism Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 4 Current Electricity and Magnetism

Class 8 Science Chapter 4 Current Electricity and Magnetism Textbook Questions and Answers

1. Write proper words from the following group of words in the blanks and rewrite the completed sentences:
(magnetism, 4.5V, 3.0V, gravitational attraction, potential difference, potential, higher, lower, 0V)

Question a.
Water in the waterfall flows from a higher level to the lower level because of …………… .
Answer:
Water in the waterfall flows from a higher level to the lower level because of gravitational attraction.

Question b.
In an electric circuit, electrons flow from a point of potential to the point of ……….. potential.
Answer:
In an electric circuit, electrons flow from a point of lower potential to the point of higher potential.

Question c.
The difference between the electrostatic potential of the positive end and the negative end of an electric cell is the …………. of the cell.
Answer:
The difference between the electrostatic potential of the positive end and the negative end of an electric cell is the potential difference of the cell.

Question d.
Three electric cells of potential difference 1.5 V each have been connected as a battery. The potential difference of the battery will be ……………… V.
Answer:
Three electric cells of potential difference 1.5 V each have been connected as a battery. The potential difference of the battery will be 4.5 V.

Question e.
An electric current flowing in a wire creates ………………… around the wire.
Answer:
An electric current flowing in a wire creates magnetism around the wire.

2. A battery is to be formed by joining 3 dry cells with connecting wires. Show how you will connect the wires by drawing a diagram.

Question a.
A battery is to be formed by joining 3 dry cells with connecting wires. Show how you will connect the wires by drawing a diagram.
Answer:

3. In an electric circuit, a battery and a bulb have been connected and the battery consists of two cells of equal potential difference. If the bulb is not glowing, then which tests will you perform in order to find out the reason for the bulb not glowing?

Question a.
In an electric circuit, a battery and a bulb have been connected and the battery consists of two cells of equal potential difference. If the bulb is not glowing, then which tests will you perform in order to find out the reason for the bulb not glowing?
Answer:
If you can see the filament of the bulb, check whether it is intact or broken. Check whether the cells are connected in a proper manner:

Or in a wrong way:
If they are connected in a wrong way as shown above, the total potential difference will be 2V + (-2V) = zero.
Figures for reference:

4. Electric cells having potential difference 2V each have been connected in the form of a battery. What will be the total potential difference of the battery in both cases?

Question a.
Electric cells having potential difference 2V each have been connected in the form of a battery. What will be the total potential difference of the battery in both cases?

Answer:
(i) 6V
(ii) 8V.
[Note: In (i), three cells are connected in series.
∴ Total potential difference = 2V + 2V + 2V = 6V.
In (ii), four cells are connected in series.
∴ Total potential difference = 2V + 2V + 2V + 2V
= 8 V]

5. Describe the construction, working and usefulness of a dry cell, with the help of a diagram.
Question a.
Describe the construction, working and usefulness of a dry cell, with the help of a diagram.
Answer:

Dry cell:
Take a lead dry cell and remove its outer coating. Inside you will find a whitish, metal layer. This is the zinc (Zn) metal layer. This is the negative terminal of the cell. Now, carefully break open this layer. There is another layer inside. An electrolyte is filled between these two layers.

The electrolyte contains negatively charged and positively charged ions. These are the carriers of electricity. The electrolyte is a wet pulp of zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl). There is a graphite rod at the centre of the cell. This is positive terminal of the cell. A paste of manganese dioxide (MnO₂) is filled outside the rod. Because of the chemical reactions of all these chemicals, electrical charge is produced on the two terminals (graphite rod and zinc layer) and an electric current flows in the circuit.

Due to the wet pulp used in this cell, the chemical reaction proceeds very slowly. Hence a large electric current cannot be obtained from this. Compared to the electric cells using liquids, the shelf life of dry cells is longer. Dry cells are very convenient to use as these can be held in any direction with respect to ground and can be used in mobile instruments such as radio sets, wall clocks and torches.

6. Describe the construction and working of an electric bell with the help of a diagram.

Question a.
Describe the construction and working of an electric bell with the help of a diagram.
Answer:
Figure shows the construction of an electric bell and also the electric circuit. The bell consists of an electromagnet, contact screw, iron strip, metal striker and metal gong. A coil of copper wire wound around an iron piece works as an electromagnet and an iron strip along with a striker is fitted near it. A contact screw touches the strip.

The circuit is closed with the key. The current flows in the circuit when the screw is in contact with the iron strip. The current – carrying coil becomes a magnet and attracts the iron strip towards it. As a result, the metal striker hits the metal gong producing sound. At the same time, the screw loses the contact with the strip. The circuit is now incomplete.

Hence, no current flows in the circuit. Therefore, the electromagnet loses its magnetism and the electric iron strip returns to its initial condition, making contact with the screw. As the circuit is now completed, the electromagnet attracts the iron strip and the striker strikes the gong producing sound.

The action repeats itself and the bell continues to ring till the circuit is broken by opening the key in the circuit.
The working of the electric bell is thus based on the magnetic effect of electric current.

Project:

Present all the activities that you performed in this chapter in Science exhibition.

Class 8 Science Chapter 4 Current Electricity and Magnetism Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
The SI unit of electric charge is the ……………… .
Answer:
The SI unit of electric charge is the coulomb.

Question 2.
The SI unit of electric current is the ……………… .
Answer:
The SI unit of electric current is the ampere.

Question 3.
The SI unit of electric potential is the ………………. .
Answer:
The SI unit of electric potential is the volt.

Question 4.
1 ampere = 1 coulomb per …………… .
Answer:
1 ampere = 1 coulomb per second.

Question 5.
When a glass rod is rubbed on a silk cloth, the glass rod acquires …………… charge.
Answer:
When a glass rod is rubbed on a silk cloth, the glass rod acquires positive charge.

Rewrite the following statements selecting the correct options:

Question 1.
The potential difference between the two electrodes of the lead-acid cell is nearly ………………. .
(a) 1 V
(b) 1.2 V
(c) 1.5 V
(d) 2 V
Answer:
(d) 2 V

Question 2.
The Ni-Cd cell delivers a potential difference of …………….. .
(a) 1 V
(b) 1.2 V
(c) 1.5 V
(d) 2 V
Answer:
(b) 1.2 V

Question 3.
…………….. is a scalar quantity.
(a) Force
(b) Acceleration
(c) Velocity
(d) Electric current
Answer:
(d) Electric current

Question 4.
The working of an electric bell is based on ………….. .
(a) the heating effect of electric current
(b) the chemical effect of electric current
(c) the magnetic effect of electric current
(d) the optical effect of electric current
Answer:
(c) the magnetic effect of electric current

Question 5.
The coulomb is the SI unit of electric ………….. .
(a) current
(b) resistance
(c) potential
(d) charge
Answer:
(d) charge

State whether the following statements are True or False:

Question 1.
The SI unit of electric potential is the ampere.
Answer:
False. (The SI unit of electric potential is the volt. OR The SI unit of electric current is the ampere.)

Question 2.
In the external circuit, the conventional current flows from the positive terminal of the cell to the negative terminal of the cell.
Answer:
True.

Question 3.
Very small current flows when lightning occurs.
Answer:
False. (A large current flows when lightning occurs.)

Question 4.
Sensation is felt by us due to a microscopically small current flowing to the brain.
Answer:
True.

Question 5.
In a car battery, a current is produced by the flow of both negatively and positively charged particles.
Answer:
True.

Identify the odd term:

Question 1.
Pressure exerted by a liquid, Electric current, Electric potential difference, Buoyant force.
Answer:
Buoyant force. It is a vector quantity. Others are scalar quantities.

Question 2.
Electric bulb, Electric heater, Electric bell, Electric iron.
Answer:
Electric bell. Its working is based on the magnetic effect of electric current. The working of other devices is based on the heating effect of electric current.

Answer the following questions in one sentence:

Question 1.
State the relation among the SI units of electric current, electric charge and time.
Answer:
1 ampere = 1 coulomb per second.

Question 2.
Name the positive terminal of the dry cell.
Answer:
The graphite rod at the centre is the positive terminal of the dry cell.

Question 3.
What constitutes an electric current in a metal?
Answer:
A continuous flow of electrons constitutes an electric current in a metal.

Question 4.
What is a battery?
Answer:
A group of two or more cells connected in series to obtain more potential difference is called a battery.

Question 5.
What is a solar cell?
Answer:
A solar cell is a device that converts solar energy into electrical energy.

Question 6.
State one characteristic of the Ni-Cd cell.
Answer:
The Ni-Cd cell is rechargeable.

Question 7.
Give one example in which the magnetic effect of electric current is used.
Answer:
The working of an electric bell is based on the magnetic effect of electric current.

Answer the following questions:

Question 1.
When do we get current electricity?
Answer:
We get current electricity when charged particles such as electrons, positive ions and negative ions are made to flow in a conductor by applying electric force.

Question 2.
Explain the concept of electrostatic potential (electric potential).
Answer:
A liquid flows from a higher level to a lower level. Heat flows from a body at a higher temperature to a body at a lower temperature. Also when different parts of a body are at different temperatures, heat flows from the part at a higher temperature to the part at a lower temperature.

Similarly, a positive charge (free to move) flows from a point at a higher electric level to a point at a lower electric level and a negative charge (free to move) flows from a point at a lower electric level to a point at a higher electric level. The electric level deciding the direction of flow of electric charge is called electrostatic potential (electric potential).

Question 3.
What is the SI unit of electric potential?
Answer:
The SI unit of electric potential is the volt (V).
[Note : This unit is named in honour of Alessandro Volta (1745-1827), Italian physicist, the inventor of the electric battery.]

Question 4.
What is potential difference?
Answer:
Potential difference is the difference
between the potentials at two points. It is similar to the height of a waterfall or the temperature difference between a hot body and a cold body. Potential difference is expressed in volt.

Try this: 

Take connecting copper wires and connect the ‘circuit’ as shown in Fig.(a). No current is seen to flow in the bulb. Now connect in the same ‘circuit’ a 1.5 V dry cell available in the market as shown in Fig.(b). Now it will be realized from glowing of the bulb that a current is flowing in the circuit. Electrons in the wire flow due to the potential difference between the two ends

In Fig.(a), there is no current as ) there is no potential difference in the absence of any cell. Current starts flowing in the circuit as soon as the potential difference is applied. The unit of potential difference in SI system is the volt (V). We will learn about it in the next standard.

Question 5.
What is electric circuit or electrical circuit?
Answer:
A continuous path consisting of conducting wires, a switch or a plug key and other resistances (for example, resistance of an electric bulb) between the terminals of a cell (or a battery) along which an electric current flows is called an electric circuit.

Question 6.
What is electric current?
Answer:
Electric current is the electric charge flowing through a conductor, such as a metal wire, per unit time.

Question 7.
What is one ampere?
Answer:
If one coulomb of charge is passing through any cross section of a conductor in one second, the amount of current flowing through it is called one ampere.
[Note: 1 ampere = 1 coulomb per second OR 1A = 1 C/s. The coulomb is named in honour of Charles Augustin de Coulomb (1736 – 1806), French physicist. The ampere is named in honour of Andre Ampere (1175 – 1836), French physicist and mathematician.]

Think about it:

Question a.
How can we measure water flow emerging from a pipe? We can find it from the amount of water (litres) coming out in a specific time period. How then is the electric current measured?
Answer:
Electric current, I = Q/t. In principle, if we can measure the quantity of charge (Q) flowing through a cross section of a conductor in time t, we can determine the current (i) using this formula (for a steady current). In practice, this is not done. Usually, electric current is measured using the magnetic effect of electric current. One can also use the heating effect and chemical effect of electric current for measurement of electric current.

Question 8.
What is an electric cell? What is its main function?
Answer:
An electric cell is a general device used to produce a uniform flow of charges in a circuit. Its main function is to maintain a constant potential difference between its two terminals.

Question 9.
Name ten devices in which electric cells are used.
Answer:
Electric cells are used in radio sets, wall clocks, wrist watches, torches, toys, mobile phones, cars, invertors, remote controls, ships, submarines, satellites, etc.

Question 10.
Draw a neat labelled diagram to show the design of the lead-acid cell and explain its principle of working.
Answer:
The lead-acid cell contains two electrodes, Pb and PbO₂, dipped in dilute H₂SO₄. Chemical reaction between the substances in the cell produces electric charges on the electrodes. PbO₂ carries a positive charge and Pb carries a negative charge. The potential difference between the electrodes is nearly 2V.

If a load, such as a bulb, is connected externally between the two electrodes, an electric current flows through it. It can deliver a large current. This cell can be recharged after getting electrically discharged.

Question 11.
State applications of the lead-acid cell.
Answer:
Lead-acid cells are connected in series to obtain higher potential difference. The lead-acid battery is used in cars, trucks, motorcycles and uninterrupted power supplies (UPS).

Question 12.
What is the potential difference delivered by the Ni-Cd cell?
Answer:
The potential difference delivered by the Ni-Cd cell is (about) 1.2 V.
[Note: In this cell, nickel oxide is the positive electrode and cadmium is the negative electrode. It is often used as a dry cell and it can be recharged. These cells are used in some portable machines that run on electricity like a drilling machine or a gardening tool.]

Question 13.
Draw a neat labelled diagram of a simple electric circuit containing a cell, an electric bulb and a plug key. What happens when the key is (i) open (ii) closed?
Answer:

(i) When the key is open, there is no current in the circuit. Hence, the bulb does not glow.
(ii) When the key is closed, a current flows in the circuit. Hence, the bulb glows.

Figure for reference:
Here, six cells can be connected in series to obtain more potential difference.

Research:
Lithium ion cells are used in modern equipment for example, a smart phone, laptop, etc. These cells can be recharged. More electrical energy can be stored in these cells as compared to that in Ni-Cd cells.

Question 14.
See Fig. What is the potential difference between A and B if each cell delivers a potential difference of 2V?

Answer:
Potential difference between A and B
= 2V + 2V + (-2V) + 2V = 4V.

Use your brain power!

Question a.
You must have seen the car battery available in the market. It is called a battery and not a cell. Why?
Answer:
In a car battery, a number of cells are connected in series to obtain more potential difference.

Here, two identical cells are connected in parallel. The potential difference between A and B is 2V. This arrangement can be used for a longer time compared to a single cell.

Series and parallel arrangement for higher potential difference and longer life.
Here, the potential difference between A and B is 8V.

Try this:

Magnetic effects of electric current :
Activity 1 :
Take the inside tray of a used up matchbox. Place a small magnetic needle inside the tray. Now take a long connecting wire and wind it around the tray. Complete the electric circuit by connecting in it, this wire, electric cell, plug key and a bulb Figure.

Mark the position of the magnetic needle. Take a bar magnet near to the magnetic needle.
1. What do you observe? Keep looking at the needle and close the plug key. The bulb will light up, and you will realize that the current has started flowing.
2. Does the magnetic needle change its position? Now open the plug key.
3. Does the magnetic needle come back to the original position?
4. What will you conclude from this experiment?
You know that a magnetic needle is indeed a magnet. You have seen that the magnetic needle changes its direction when a bar magnet is taken near the magnetic needle. Also, you have observed that the magnetic needle changes its direction when a current starts flowing in the circuit. This means that magnetic field is created when an electric current flows in a wire. Hans Christian Oersted made this observation first. Briefly we can say that when an electric current passes through a wire, a magnetic field is produced around that wire.
Answer:

1. The magnetic needle is deflected.
2. Yes.
3. Yes.
4. The electric current produces a magnetic field around a current-carrying conductor.

Activity 2 :
Take a metre long flexible copper wire having resistive coating and wind it tightly on a long iron screw. Connect the two ends of the wire in a circuit as shown in the Figure. Also connect an electric cell and a plug key in the circuit. Keep 2-4 iron pins/small nails near the screw. Now start the current in the circuit by plugging the key. It will be noticed that the pins/nails have stuck to the tip of the screw. Will the pins/nails continue to stick when the plug key is opened?

Answer:
No.
When the electric current flows in the wire, magnetism is produced in the coil around the screw and because of that the screw also attains magnetism. As soon as the current is stopped, this magnetism vanishes. The system of the coil and the screw is called an electromagnet. You have seen various uses of the electromagnet in the sixth standard. Electromagnets are used to produce a strong magnetic field useful in scientific research.

Question 15.
What is an electromagnet? State ! its applications.
Answer:
If a coil is wound around an iron screw (or an iron rod) and a current is passed through the coil with a cell (or a battery), the screw behaves as a magnet as long as there is current in the coil. The i system of the coil and the screw is called an electromagnet. It is an example of magnetic effect of electric current.
Applications: Electric bell, cranes for moving heavy loads from one place to another, toys that run on electric cells.

Question 16.
How can the strength of an electromagnet be increased?
Answer:
The strength of an electromagnet can be increased by increasing the current producing the magnetic field.

Question 17.
What is the use of the elastic iron strip in the electric bell?
Answer:
Due to the elastic iron strip, the making and breaking of the circuit occur alternately and the bell continues to ring as long as the key in the circuit is closed.

Question 18.
What will happen if the elastic iron strip in the electric bell loses its flexibility?
Answer:
When the circuit breaks and the electromagnet loses its magnetism, the strip, due to loss of flexibility, will not return to its normal position of contact with the screw. Hence, the circuit will not be completed and the bell will not ring.

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 8 Pollution Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 8 Pollution

Class 8 Science Chapter 8 Pollution Textbook Questions and Answers

1. Following are some statements about pollution. Which type of pollution do those express:

Question a.
Fog seems to be appearing in Delhi during day hours.
Answer:
Air pollution-Smog
(The sentence should have the word Smog and not fog. Smog is fog with smoke. Only fog cannot be polluting, but the smog is.)

Question b.
Many times, vomiting and dysentery occurs after eating ‘panpuri’.
Answer:
Water pollution-Contaminated food and water due to bacteria or virus

Question c.
Problem of sneezing occurs sometimes during visit to garden.
Answer:
Air pollution due to pollens

Question d.
Crop does not grow up in some areas.
Answer:
Soil pollution

Question e.
People living in the busy squares face the problems like short breathing and other respiratory problems.
Answer:
Air pollution due to traffic

2. Read the passage and identify the sentences expressing types of pollution.

Question a.
Nilesh is a student of Std. VII and lives in urban area. It takes about an hour to go to the school by bus. He faces the heavy traffic of two wheelers, four wheelers, rickshaws, buses while going to school. He is facing the problem of asthma since last few days, Doctors recommended him to stay away from urban area. Since then, his mother sent him to the village of his maternal uncle, Nilesh saw the heaps of garbage at many places in village. Foul smell of human and animal wastes was present at many places. Blackish water with foul smell was flowing in a stream. He developed some abdominal disease within few days.
Answer:

1. It takes about an hour to go to the school. (Due to traffic jam, Nilesh is spending more time in polluted, contaminated air.)
2. He faces the heavy traffic. (Large scale combustion of fossil fuel.)
3. He is facing the problem of asthma. (Air pollution – Harmful to human health.)
4. The heaps of garbage at many places. (Solid waste – Land pollution.)
5. Foul smell of human and animal wastes. (Biological pollution, air pollution.)
6. Blackish water with foul smell was flowing in a stream. (Improper sewage management – Water pollution.)
7. He developed some abdominal disease within few days. (Water pollution – Effect on human health.)

3. Match the pairs from ‘A’ and ‘B’ columns and explain the effect of pollution on human health.

Question a.

Answer:

4. True or false.

Question a.
Water does not get polluted by washing the clothes in running water of river.
Answer:
False. (Even if washing of soiled clothes is done in running water, it will cause pollution as the dirt and the waste materials will be added to water. This certainly will cause water pollution.)

Question b.
More the use of electric appliances, more will be the pollution.
Answer:
True. (Most of the electricity is generated in India by burning coal. The power generation plants thus cause lots of air pollution. More the electricity is used by using more appliances, there will be more pollution. However, only power generation through solar energy cannot cause pollution.)

5. Answer the following:

Question a.
What is pollution?
Answer:
Contamination of natural environment that can harmfully affect the environment is called pollution.

Question b.
What are Pollutants?
Answer:
The products which affect the normal functioning of ecosystem and have an adverse effect on plants, animals and humans are called pollutants.

Question c.
What is acid rain?
Answer:
1. When rainwater contains harmful amounts of nitric and sulphuric acids, it is called acid rain.
2. Burning of fossil fuels such as coal, wood, petroleum, etc. releases nitrogen oxide and sulphur oxide into the atmospheric air.
3. Since these oxides are soluble in water, they dissolve in rainwater. Nitrogen and sulphur oxides dissolved in large quantities of water vapour form acids like nitric acid, nitrous acid, sulphurous acid and sulphuric acid.
4. These acids mix with mist, drops of rainwater and snow. They change their composition and fall back on the ground in the form of acid rain.
5. Effects of acid rain are as follows:

• Increase in the acidity of soil and water bodies.
• Damage to the trees.
• Water becomes unsuitable for fish and wildlife.
• Buildings, statues, sculptures, bridges, monuments and fences are corroded due to acid rain. Thus, acid rain damages our national assets.
• Acid rain affects agriculture and crop lands.

Question d.
What is greenhouse effect?
Answer:

1. Greenhouse effect is the ; phenomenon due to which global warming and climate change occur.
2. The earth receives solar energy in the form of heat from the sun. The surface of earth absorbs this heat and reflects it back to the atmosphere as infrared radiation. Some of this heat energy goes directly into space.

Question e.
Which are visible pollutants known to you?
Answer:
1. The polluting substances that are seen easily with the naked eyes can be called as visible pollutants. E.g. Solid wastes, plastic articles, plastic bags, the suspended things in the water, metal refuse, etc.

Question f.
Which are invisible pollutants?
Answer:
The pollutants which are completely dissolved in water or mixed in the air, cannot be seen and hence they can be called invisible pollutants. Since they are not seen, we remain unaware about the presence of these pollutants. E.g. the insecticides spread f on the crops. Aerosols, many hazardous gases in the air, toxic compounds that are totally soluble in water, etc.

6. Answer the following.

Question a.
Give two examples of each of water, soil and air pollution from your residential area.
Answer:
Air pollution:

1. New buildings are constructed. Old structures are demolished. This is creating lots of dust pollution. The air is full of particulate matter.
2. The number of vehicles on the road has tremendously increased. This causes smoky environment.

Water pollution:

1. The sea shows lots of floating plastic and decaying flowers, etc. When beaches are visited it is a common sight.
2. Many fishes are seen dying in great numbers and are washed off to the shore.

Soil pollution :

1. Everywhere garbage heaps are seen. In that plastic bags, needles, old medicine vials and cartons are seen in abundance.
2. The sludge brought by rainwater is spread everywhere and that causes stink.

Question b.
How does the pollution occur due to vehicles? Give the names of vehicles causing least pollution.
Answer:

1. More than 50% of the air pollution is caused by vehicular traffic.
2. Particulate matter, unburnt hydrocarbons, CO, nitrogen oxides and carcinogenic hydrocarbons are present in the automobile exhausts.
3. Fossil fuels like petrol, diesel, natural gas, gasoline, etc. which are burnt to run the automobiles lead to the emission of CO₂ and other gases.
4. Therefore, vehicles are said to be the major contributors to air pollution.
5. The only vehicle which is non¬polluting is bicycle. The four-wheelers which are battery operated are also manufactured recently.

These two types of vehicles are eco-friendly. The cars that run on C.N.G. are also said to be lesser polluting.

Question c.
What are natural reasons causes for water pollution?
Answer:
The natural causes of the water pollution:
1. If organic pollutants are added to the water there is an overgrowth of weeds such as Eichhornia. The growth of algae also makes the water unsuitable for consumption. These aquatic plants release oxygen during daytime but by night they require oxygen thus depleting the dissolved oxygen level. The natural characters of water are then changed.

2. The decomposing matter when added to the water make it polluted and stinking.

3. Due to deposition of sludge or eroded soil, the rivers change their path and divert from original flow. The currents are also changed. Deposition of sludge makes the water polluted.

4. Due to soil erosion, surrounding the water bodies, the microbes, bacteria, protozoans and the worms and larvae of nematodes enter the water causing severe biological pollution. Many inorganic pollutants are also added to the water. The fungand bacteria present in the water make it non-potable. Such water spreads water-borne diseases.

Question d.
Suggest four preventive measures for air pollution.
Answer:
The following methods are adopted to control air pollution from the industries:

1. The source discharge is diluted by tall chimneys.
2. There are source correction methods like changing the raw material, equipment modification, process modification, etc.
3. Effective pollution controlling equipment like dust collectors, electrostatic precipitators, wet scrubbers, etc. should be used.
4. There should be ban and control over atomic tests and chemical weapons on the international level.

Question e.
Explain relation between greenhouse effect and global warming.
Answer:
Because of greenhouse effect, there is increase in the global temperature. The heat on the earth remains trapped due to envelope of greenhouse gases. The percentage of carbon dioxide and methane is constantly increasing and hence there is increase in the temperature too. Thus the greenhouse effect is directly related to the global warming.
Effects of this relation between greenhouse effect and global warming are as follows:

1. The polar ice caps and the glaciers at both the poles are melting due to increased temperature.
2. The oceans’ water is rising due to this melted ice. The sea level rise is causing coastal land submergence. The islands at various regions are threatened of drowning.
3. Many species of living organisms are already extinct due to global warming. The rest are also threatened.
4. Wild animals are showing weird migrations. Polar bear is endangered.
5. The increased temperature of the oceanic water is causing many changes in the tides and currents. This results into increased occurrence of cyclones, hurricanes and cloud bursting. The natural disasters are rising in last decade.
6. The agricultural production is decreasing. The regions with less rainfall are facing draughts.

Question f.
Construct two slogans each on air, water and soil pollution.
Answer:
Air pollution:

1. Be a part of the solution and not part of pollution.
2. Show your care, clean your air.

Water pollution:

1. Water, water everywhere, Not a drop to drink. The pollution is making all the water stink.
2. Save the fish and the little turtle. Don’t throw plastic or it will encircle.

Soil Pollution:

1. Don’t be mean, keep environment clean.
2. Let’s keep land clean, together only we can win.

7. Classify the following pollutants into natural and manmade categories.

Question
Classify the following pollutants into natural and manmade categories.
Sewage, dust, pollen grains, chemical fertilizers, vehicular smoke, algae, pesticides, waste of animals and birds.
Answer:

Project:

Question 1.
Visit the water testing laboratory in your area and collect the information about tests for checking the purity of water.

Question 2.
Visit the square having heavy traffic in your area and report the pollution at different times of day and find out the duration of maximum pollution.

Class 8 Science Chapter 8 Pollution Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
Natural pollutants are destroyed in due course of time by …………. .
Answer:
Natural pollutants are destroyed in due course of time by nature’s rule.

Question 2.
Air pollutants with ……….. cause colour change in paints, oil paintings, nylon, etc.
Answer:
Air pollutants with sulphur cause colour change in paints, oil paintings, nylon, etc.

Question 3.
Boards indicating the …………. are displayed in busy squares in metro cities.
Answer:
Boards indicating the air quality index are displayed in busy squares in metro cities.

Question 4.
Soil ………… decreases due to pollution.
Answer:
Soil fertility decreases due to pollution.

Question 5.
Problem of …………… pollution increases due to soil pollution.
Answer:
Problem of water pollution increases due to soil pollution.

State whether the following statements are True or False. Explain your statement:

Question 1.
Polluted water is responsible for diseases such as cholera, hepatitis, typhoid, skin diseases and diseases of the alimentary canal.
Answer:
True. (The water sources if they are contaminated with biological pollutants such as bacteria, viruses or protozoans, can cause variety of water-borne diseases.)

Question 2.
When water is mixed with natural or artificial unwanted material, the dissolved oxygen level of such water increases.
Answer:
False. (When water is mixed with natural or artificial unwanted material, the dissolved oxygen level of such water decreases. This causes harm to the resident animals. However when aquatic weeds and algae outgrow in number it causes rise in oxygen only during day time.)

Question 3.
Though any amount of pollutants are added to the soil, the toxic substances do not leach into water.
Answer:
False. (The toxic substances added to the soil can leach in the groundwater and cause water pollution.)

Identify the odd term:

Question 1.
Industrialization, Population explosion, Mining, Vehicular transport, Dust storms.
Answer:
Dust storms (All others are man-made causes environmental degradation.)

Question 2.
Poisoning, asthma, Silicosis, respiratory diseases.
Answer:
Silicosis (All others are effects of methane.)

Question 3.
Irritation of eyes, respiratory tract, excess mucus, mental weakness
Answer:
Mental weakness (All other are effects of sulphur dioxide.)

Question 4.
Volcanic eruption, Earthquake, Atomic explosion, Forest fires.
Answer:
Atomic explosion (All others are natural causes of air pollution.)

Question 5.
Uranium, Sulphur, Thorium, Plutonium.
Answer:
Sulphur (All others are elements which are used in the production of atomic energy.)

Consider the relation between the items in the first pair and write the correlation for second pair:

Question 1.
Industrialization: Sulphur compounds : :…………………. : Lead compounds
Answer:
Use of fuels/Transportation

Question 2.
City where smoke and soot caused it to be called black city : Petersburg : : Indian city where worst ever industrial accident has occurred : ……………….
Answer:
Bhopal

Question 3.
Arsenic and Cadmium : Inorganic water pollutants : : Weedicides and insecticides : ………….
Answer:
Organic water pollutants.

Write definitions:

Question 1.
Air pollution.
Answer:
Contamination of air by toxic gaseous and particulate pollutants in concentration which is harmful to human beings and his surroundings is called air pollution.

Question 2.
Water pollution.
Answer:
When toxic and unwanted substances enter, dissolve or remain suspended in the water bodies deteriorating the quality of water and affecting the aquatic ecosystem, then it is known as water pollution.

Question 3.
Soil pollution.
Answer:
Soil pollution is the phenomenon caused due to natural or man-made causes, which occurs when there are changes in its physical, biological and chemical properties of the soil leading to decreased fertility due to either natural or man-made reasons.

Distinguish between the following:

Question 1.
Degradable and Non-degradable pollutants:

Question 2.
Industrial waste and Domestic waste:

Give scientific reasons:

Question 1.
Domestic sewage is harmful for all forms of life.
Answer:

1. Domestic sewage contains water
2. There are detergents and washing private vehicles. powders containing phosphate, which are used to soften the water.
3. These chemicals are harmful to aquatic animals.
4. They also contain disease. causing pathogenic bacteria and viruses.
5. Hence, domestic sewage is harmful for originating from kitchen, bathrooms, toilet, forms of

Question 2.
Use public transport instead of private vehicles.
Answer:

1. All the automobiles use fossil used to soften the water. fuels Burning of fossil fuels causes air pollution by gaseous pollutants as well as by particulates.
2. Toxic gases such as CO, CH₄, SO₂, etc. are emitted through automobile exhausts.
3. When each person uses private vehicles, the proportion of air pollution increases.
4. Instead, public transport helps to reduce air pollution it will also help to ease trafficams.
5. Therefore, as a role of citizen in pollution control, public transport should be used instead of private vehicles.

Question 3.
Due to agriculture, there can be a lot of air pollution.
Answer:

1. During agricultural practices, open field burning is done. Due to this burning there is emission of gases like SO₂, CO₂, CH₄, CO and oxides of nitrogen along with large amounts of particulate matter.
2. In agricultural practices, pesticides used emit toxic chemicals.
3. Industrial farms pollute air by emitting foul odour and airborne pollutants.
4. When manure is decomposed, there is production of greenhouse gases.

Question 4.
A hole has been observed in the ozone layer in the stratosphere near Antarctica.
Answer:

1. Ozone layer depletion is mainly caused due to the action of CFC (Chlorofluorocarbon) molecules in the air.
2. Due to various increased activities of humans, the magnitude of air pollution has been increasing in the last few decades.
3. CFC molecules were used as coolants in refrigerators, freezers and air conditioners.
4. They were also present in industrial solvents, dry cleaning agents and hospital sterilants, aerosols and foam. Due to such enhanced use, much of the CFCs were liberated in the last few years.
5. CFC molecules are decomposed by ultraviolet rays which release chlorine and fluorine molecules.
6. Chlorine and fluorine react with the ozone resulting in a hole in the ozone layer present in the stratosphere.

Therefore, a hole has been observed in the ozone layer in the stratosphere above Antarctica.

Answer the following.

Question 1.
What do you mean by ozone layer depletion? What are the causes of ozone layer depletion?
Answer:
1. The ozone layer is present at the top of the stratosphere. The stratosphere is the second layer of the atmosphere which is present 48 km above the earth’s surface.
2. Ozone layer is protective layer for living organisms of the earth, as it absorbs harmful UV rays from the sun. When this layer is reduced or destroyed, it is called ozone layer depletion.

3. Causes of the ozone layer depletion:

1. The main cause of ozone depletion are CFC molecules.
2. Chlorine atoms are present in chlorofluoro-carbons (CFC) molecules. They react with ozone and deplete it.
3. CFCs are used as coolants in refrigerators, freezers and air conditioners manufactured before 1995.
4. CFCs are also present in industrial solvents, dry cleaning agents and hospital sterilants (sterilizers), aerosols and foam. All the above materials release a lot of CFCs into the atmosphere.
5. CFC molecules are broken down by ultraviolet radiations which result in release of chlorine and fluorine, which further reduce the ozone layer.

Question 2.
What adverse effect does ozone depletion have?
Answer:

1. When the ozone layer is depleted, the ultraviolet radiations of the sun can reach the earth’s surface in greater proportion.
2. This results in damage to animal and plant life on the earth.
3. Ultraviolet rays cause skin cancer and cataract in human beings.
4. The ozone hole is seen in the stratosphere above Antarctica.

Question 3.
Describe the effects of air pollution on animals and plants.
Answer:
1. Effects of air pollution on animals:

• Air pollutants affect breathing of the animals.
• Particulate pollutants can cause problems to the wildlife.
• Particulate matter containing heavy metals is accumulated in the bodies of animals. The accumulated heavy metals at high levels in the body tissues, can cause problems. ‘
• Acid rain causes serious problems to animal life.

2. Effects of air pollution on plants:

• Various parts of the plant show reduced growth after coming in contact with air pollutants.
• The leaves show yellowing or chlorosis on exposure to air pollutants.

Question 4.
What are man-made reasons for water pollution?
Answer:
The effluents and other substances released by man into the surrounding water bodies together can be called man-made reasons for water pollution.
1. Domestic sewage: The excreta, urine and other domestic-use water is added to the water bodies in many cities and villages. In big metro-cities, the sewage is partially treated but these management practices are not enough.

2. Industrial effluent: Different industries and factories release effluents which may contain toxic and harmful components, such as various pigments, bleaching chemicals, leather pieces, fibres, mercury, lead, etc.

3. Oil pollution: Oil spillages are seen in the seas due to leakage of crude oil. The crude oil is hazardous as it contains cancer causing hydrocarbons.

4. Fertilizers and pesticides: These compounds when used in farm, may get washed off to nearby water body. The chemical fertilizer containing N, P, K cause water pollution. Pesticides such as endrin, chlorine, carbonate containing pesticides, etc. are mixed with water. They cause contamination of the aquatic animals.

5. The wrong behaviour of human beings causes water pollution. The addition of wastes, defecation near coasts, washing clothes, decomposing hemp and flax in water, disposal of ashes, floral offerings to god, dumping ashes all such activities result into water pollution.

6. The warm water released into the water body through thermal power plants cause thermal pollution.

Question 5.
What are the effects of water pollution on human beings?
Answer:
The water-borne diseases that are caused by different bacteria and viruses cause infections to human beings through contaminated water. Some bacterial and viral diseases are spread through epidemics. Cholera, hepatitis, enteritis, diarrhoea, typhoid are such diseases that can cause severe infections to man. Polluted water also cause skin diseases and deformities of bones, Some pollutants accumulated in vital organs cause their ailments. Liver, kidneys, brain, etc. are affected in this way. Person may develop hypertension too due to pollutants.

Question 6.
What are the effects of water pollution on the ecosystem?
Answer:
Biological effects:

1. Plants in the ecosystem show retarded growth, resulting into species loss.
2. Due to imbalance in the ecosystem, the food chain and food web is disturbed.
3. Pollutants cause mortality in fish and other aquatic animals.
4. Oil slick causes harmful impact on the marine birds.
5. Useful bacterial fauna in the water is lost.

Abiotic effects:

1. Pollutants cause changes in physical and chemical properties of water.
2. Salinity of the water changes.
3. Dissolved oxygen in the water is depleted, causing mortality of fishes.

Question 7.
Describe the effects of air pollution on the environment.
Answer:
Air pollution can cause the following serious effects on the environment:

1. Deforestation and fuel consumption bring about rise in CO₂ concentration.
2. Excess CO₂ in air causes rise in atmospheric temperature of the earth.
3. The increased temperature is called global warming.
4. The global warming results into melting of glaciers, subsequently causing rise in the sea level.
5. There is a change in the climate and pattern of rainfall. This may indirectly affect the agricultural production.

Question 8.
Describe the effects of soil pollution.
Answer:
Effect of soil pollution:

1. There are many pathogenic bacteria, viruses and parasitic intestinal worms in the sewage sludge. These are able to cause many diseases.
2. Soil and vegetable crops are contaminated by manure made from human and animal excreta containing pathogens. This can lead to various diseases.
3. There is loss of fertility and productivity of soil and land due to soil pollution.
4. Soil pollution leads to water pollution, when toxic chemicals leach into the groundwater. Similarly, when contaminated soil enters into streams or lakes, it also causes water pollution.
5. Radioactive materials and soil contaminants can travel through food chains. They move away from the soil into crops, livestock and human bodies.

Question 9.
How do biodegradable and non- biodegradable wastes cause land pollution?
Answer:

1. Biodegradable material is mainly present in the domestic waste.
2. It is in the form of food waste, peels of fruits, vegetables, etc.
3. Paper is also a main part of the domestic waste which is biodegradable.
4. Polythene bags, plastic waste and footwear, etc. are non-biodegradable waste from the domestic sources. All of these pollute the land.

Question 10.
How do you protect soil from being polluted?
Answer:

1. We should not throw domestic waste and industrial waste indiscriminately on the land, so that it contaminates soil.
2. Proper disposal of solid wastes and more importantly safe disposal of biomedical waste material should be practised.
3. Instead of throwing non-biodegradable materials on the land, they should be properly recycled and reused.
4. Biodegradable materials should be composted and converted into useful manure, rather than throwing them to cause pollution of the soil.
5. Excessive use of fertilizers and pesticides should be avoided so that the soil does not get contaminated.

Question 11.
What are the different laws to prevent pollution?
Answer:
The different laws to prevent pollution are as follows:

1. Water (Prevention and Control of Pollution) Act, 1974.
2. Air (Prevention and Control of Pollution) Act, 1981.
3. Environment (Protection) Act, 1986.
4. There are different laws and rules which have been made for the disposal of hazardous waste, biomedical waste, solid waste and prevention of noise pollution.

Question 12.
Who implements the laws related to pollution?
Answer:
The Central Pollution Control Board (CPCB) and Maharashtra Pollution Control Board (MPCB) check whether the organizations like factories, industrial estates, Municipalities, Zilla Parishads, Panchayat Samities and Gram Panchayats follow all the laws related to control of pollution.

Use your brain power!

Question 1.
Which types of pollutants are observed?
Answer:
Pollutants are of many varied types. They can be classified according to their sources, according to which ecosystem they are polluting, and according to their characteristics.

Question 2.
Whether the pollutants are degradable or non-degradable?
Answer:
Some pollutants are biodegradable while some are non-biodegradable. The pollutants that spread in the air are in the form of gases or particulate matter. Though they are non-degradable, they constantly make chemical reactions with each other.

The pollutants thrown in water and on land are of both the types. Pollutant like plastic is totally non-biodegradable. The biodegradable substances can be decomposed by various bacteria and fungand are converted back into elemental form. The pollutants added in S the water are also of two types. The heavy metals and colours are non-degradable.

Think about it:

Question 1.
If natural materials are pollutants, why do we not perceive their adverse effects during their use? When such materials are referred as pollutants?
Answer:
The natural pollutants are active only for a short duration. Due to natural reasons their activity is limited, and they are lost after a specific time. Their sources are not continuous and their spread too is not regular as in case of man-made pollutants which are emitted steadily.

Thus, we can avoid these substances. We also use them in limited quantity. Therefore, the natural substances, though may be polluting in nature, we are unable to perceive its toxicity. However, if we use them in abundance and create an imbalance, then its effect can be experienced as a great hazard.

Question 2.
What are the reasons other than those mentioned on the textbook page no. 55 mentioned responsible for air pollution?
Answer:
1. The automobile vehicles like two-wheelers and four-wheelers are increasing tremendously in numbers. This uncontrolled number of vehicles and their heavy traffic is causing air pollution to very high level in megacities.
2. Construction industries, demolition of the old buildings, digging the roads, are such activities which are adding to the particulate air pollution of the cities.
3. The bursting of firecrackers on the occasion of festivals and ceremonies, the spread of gulal during processions are also actions which result into unwanted air pollution.
4. Aeroplane traffic, rocket launching, industrial farming are the modern sources of air pollution.

Question 3.
Whether the vehicles with two- stroke engine cause more pollution than four stroke engine?
Answer:
Yes, they do. Scooters and motor cycles are more dominant source of air pollution as they emit soot and organic particles. In urban areas this proportion is high. These particles are toxic and they create heavy air pollution.

The two-wheelers have two-stroke engines. Such engines are far less efficient in burning the fuel that is used in the vehicles. The exhaust systems are also less effective at removing pollutants. On the contrary most of the four-wheelers have catalytic converters. Therefore, the exhaust fumes from scooters contain higher levels of the chemicals found in the fuel and oil they use.

The vehicles with two-stroke engine such as two wheelers emit significantly more primary organic aerosols and volatile organic compounds from incomplete burning of the fuel. They also produce significant secondary organic aerosols as gases released from the exhaust react with the air and microscopic particles of soot.

These pollutants increase the risk of heart and lung disease. Older two-stroke vehicles produced reactive oxygen molecules that are known to be potentially harmful for lung health. In recent times there is excessive use of two-wheelers which is deteriorating the air quality to great extent.

Question 4.
Give 5 examples of each of domestic waste, biological waste and agricultural waste and write in your own words about soil pollution due to those wastes.
Answer:
Domestic waste:

1. Empty containers of medicines, papers, bottles, etc.
2. Plastic
3. Glass pieces
4. Old utensils, clothes
5. Tins and cartons of used items, the discarded household items.

Biological waste:

1. Dead corpse of animals.
2. Urine and faeces
3. Peels of fruits, stalks of vegetables and fruits.
4. Food waste
5. Garlands and old bouquets.

Agricultural waste:

1. The stubs of crops after the grains are removed.
2. Cattle dung and urine
3. Some persistent amount of insecticides
4. Some amount of fertilizers
5. Empty containers, bags, cartons of insecticide, chemical fertilizers, seeds, gunny bags, etc.

Diagram based questions:

Question 1.
Given below is a diagram showing hazardous polluting event.
Explain what is this and what are its effects shown in the diagram.

Answer:
The above picture depicts the formation and effects of acid rain. The toxic gases such as SO2 , CO2 and NO2 are released through the chimneys of factories. These oxides are released in air. They get dissolved in the rainwater and reach back the earth’s surface in the form of acids. The plants, animals and houses are being damaged due to this acid rain.

Question 2.
Draw a well labelled diagram to show greenhouse effect.
Answer:

Activity based questions:

Question 1.
Discuss the issues like ‘dry waste-wet waste’ and ‘toilet in each home’ and write information in your own words.

MCQs based on practical:

Question 1.
Which fertilizers when used in excessive amounts cause soil pollution that spreads to neighbouring water bodies and cause water pollution too?
(a) Chemical
(b) Organic
(c) Artificial
(d) Compost
Answer:
(a) Chemical

Question 2.
What is the type of pollutants that are present in the industrial effluents that is released in the rivers and sea?
(a) Inorganic
(b) Organic
(c) Biological
(d) Biomedical
Answer:
(a) Inorganic

Question 3.
What grows in excess when eutrophication of the water bodies take place?
(a) Plants
(b) Algae
(c) Fishes
(d) Fungi
Answer:
(b) Algae

Question 4.
Which of the following is seen in the polluted water body?
(1) flowers used in pooja
(2) fruits
(3) fishes
(4) aquatic insects
(5) plastic bags
(6) turtles
(7) thick growth of algae
(8) light blue colour of water
(9) cattle wading in water
(10) broken idols
(a) (1) (3) (5) (6) (9) (10)
(b) (1) (2) (5) (7) (9) (10)
(c) (1) (3) (6) (8) (9) (10)
(d) (1) (2) (4) (7) (8) (9)
Answer:
(b) (1) (2) (5) (7) (9) (10)

Question 5.
Which is the easiest method to identify the polluted water?
(a) To taste the water
(b) To check the depth of water
(c) To observe colour and odour of the water
(d) To swim in the water
Answer:
(c) To observe colour and odour of the water

Formative Evaluation:

Question 1.
Which factors are responsible for pollution shown in the following pictures?

Question 2.
Compare the two neighbouring photographs.

Balbharti Maharashtra State Board Class 8 Civics Solutions Chapter 5 The State Government Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Civics Solutions Chapter 5 The State Government

Class 8 Civics Chapter 5 The State Government Textbook Questions and Answers

1. Choose the correct option and complete the statements:

Question 1.
The winter session of Maharashtra Legislature takes place at ……………… .
(a) Mumbai
(b) Nagpur
(c) Pune
(d) Aurangabad
Answer:
(b) Nagpur

Question 2.
The ……………. appoints the Governor.
(a) Chief Minister
(b) Prime Minister
(c) President
(d) Chief Justice
Answer:
(c) President

Question 3.
The right to summon the state legislature lies with the …………… .
(a) Chief Minister
(b) Governor
(c) President
(d) Speaker
Answer:
(b) Governor

2. Complete the table:

Question 1.

Answer:

3. Write short notes on:

Question 1.
The Governor:
Answer:

1. The Governor is the titular/ nominal head of the state.
2. The government of the state is run in the name of the Governor.
3. He is appointed by the President and holds the office during the pleasure of the President.
4. He appoints the Chief Minister and the Council of Ministers.
5. As the head of the state, he enjoys certain important Legislative and Executive powers.
6. He has a right to summon the session of the state legislature.
7. In case the need arises, he can issue ordinance to make the law.

Question 2.
Functions of the Chief Minister:
Answer:
The functions of the Chief Minister, as an Executive head of the state, are as follows:

1. To form an able Council of Ministers giving maximum representation to various regions and social groups.
2. To distribute portfolios considering the political experience, administrative skills, public awareness, leadership, etc. of the ministers.
3. To develop proper cooperation and coordination between Departments, resolve their conflicts and make them work effectively.
4. To lead the state, frame proper policies and implement them effectively, intervene in issues of the state and solve them for the comfort of the people.

4. Answer the following in brief:

Question 1.
Enumerate the functions of the Speaker of the Vidhan Sabha (Legislative Assembly).
Answer:
The Speaker is elected by the members of Vidhan Sabha. His functions are as follows:

1. To prepare the order of daily proceedings in the House.
2. To carry out the proceedings of the House in a disciplined manner.
3. To suspend the members for misbehaviour or misconduct.
4. To control and guide the proceedings of the House during sessions.

Question 2.
Why did the Constitution adopt a federal system for India?
Answer:

1. India is a country having large geographic expanse.
2. It has a multicultural population.
3. There is a great diversity in language, religion, ways of life and regional characteristics.
4. It would not have been possible to govern such a huge country from a centralised place. Hence, the Constitution adopted a federal system of India.

Question 3.
What are the considerations of the Chief Minister while allocation of portfolios?
OR
Formation of Council of Ministers is a challenging task for the Chief Minister.
Answer:
After the formation of the Council of Ministers, the Chief Minister has to distribute portfolios among the ministers. He has to consider following aspects:

1. Some portfolios are of prime importance while others are of secondary importance. He has to select appropriate people for each portfolio.
2. He has to consider the experience i and the efficiency of the ministers he has selected.
3. The political experience and administrative skills of the concerned ministers is also taken into consideration by him.
4. Other factors like the awareness of public issues, effective leadership, etc. are also considered by him.
5. If the government is in a coalition, he has to distribute portfolios appropriately among the constituent parties in the alliance.

Do you know?

1. At present, India has 29 Constituent States and 7 Union Territories.
2. All Constituent States have Legislative Assemblies.
3. Out of the 7 Union Territories, only Delhi and Puducherry have Legislative Assemblies (Vidhan Sabha).
4. Jammu and Kashmir, Bihar, Uttar Pradesh, Maharashtra, Karnataka, Telangana and Andhra Pradesh have Bicameral Legislatures (both the Houses).

Project:

Visit official website of the Maharashtra Government and collect information of various ministers and the working of their respective departments.

Class 8 Civics Chapter 5 The State Government Additional Important Questions and Answers

Choose the correct option and complete the statements:

Question 1.
The Indian Union has totally …………….. constituent states.
(a) 22
(b) 25
(c) 29
(d) 32
Answer:
(c) 29

Question 2.
In India, only ……………… states have Bicameral legislatures.
(a) three
(b) five
(c) six
(d) seven
Answer:
(d) seven

Question 3.
Maharashtra’s legislature conducts minimum ………………. sessions in a year.
(a) two
(b) three
(c) four
(d) five
Answer:
(b) three

Question 4.
Distinguished personalities from various fields are nominated by the ……………. to the Vidhan Parishad.
(a) Chief Minister
(b) Speaker
(c) Governor
(d) Chairman
Answer:
(c) Governor

Question 5.
When the legislature is not in session and need arises to make law, the Governor can issue ……………….. .
(a) a Bill
(b) a Proposal
(c) an Ordinance
(d) an Order
Answer:
(c) an Ordinance

State whether the following statements are True or False. Correct the False statements and rewrite:

Question 1.
States in India have been formed on the basis of population.
Answer:
False. States in India have been formed on the basis of language.

Question 2.
In exceptional circumstances, elections to Vidhan Sabha can be held before the completion of 5 years.
Answer:
True.

Question 3.
Absence of cooperation and coordination between Departments can affect the working of the government.
Answer:
True.

Question 4.
The people look at the Governor as a ‘Problem Solver’.
Answer:
False. The people look at the Chief Minister as a ‘Problem Solver’.

Question 5.
Every constituent state has a Vidhan Parishad.
Answer:
False. Every constituent state has a Vidhan Sabha.

Find and write:

Question 1.
The State having a government machinery different than other states
Answer:
Jammu and Kashmir

Question 2.
The Vidhan Bhavan of Maharashtrais located in:
Answer:
Mumbai

Question 3.
The member of Vidhan Sabha are called:
Answer:
MLA

Question 4.
Major challenges faced by Maharashtra:
Answer:
Terrorism and Naxalite movements

Question 5.
The place where the winter session of Maharashtra’s legislature is conducted:
Answer:
Nagpur.

Complete the following concept maps:

Question 1.

Answer:

Question 2.

Answer:

Explain the following concepts:

Question 1.
Session:
Answer:

1. A session is a meeting where members of both the Houses meet.
2. Maharashtra’s legislature conducts minimum three sessions in a year.
3. The budget session and monsoon session of Maharashtra is held in Mumbai while the winter session is held at Nagpur.
4. The Governor has the right to summon and conclude the session.
5. During the session, new laws are passed, existing laws are amended and out-dated laws are repealed.
6. The sessions are conducted under the leadership and guidance of the Speaker and the Chairman.

Question 2.
Council of Ministers:
Answer:

1. The Council of Ministers consists of the Chief Minister and other ministers.
2. The leader of the majority party in Legislative Assembly is appointed as the Chief Minister by the Governor.
3. The Governor also appoints the other ministers chosen by the Chief Minister to form Council of Ministers.
4. Framing appropriate laws, working for the welfare of the people, governing the state efficiently are some of the functions of the Council of Ministers.
5. The Chief Minister along with his Council of Ministers is collectively responsible to the Legislative Assembly.

Write short notes on:

Question 1.
Powers of the Governor:
Answer:
The Governor enjoys certain important Legislative and Executive powers as the head of the state.

1. The Bills passed by Vidhan Sabha and Vidhan Parishad are converted into laws only after receiving his assent.
2. He has the right to summon the session of the state legislature and to conclude it.
3. He can issue an ordinance to make law, on important subject if required, when the Legislature is not in session.
4. He appoints the Chief Minister and the other Council of Ministers.

Explain the following statements with reasons:

Question 1.
The Governor is the titular/nominal head of the state.
Answer:

1. The Constitution has granted Executive powers to the Governor as the head of the state.
2. The government of the state is run in the name of the Governor.
3. But in reality, the administration is carried out by the Chief Minister. Hence, the Governor is the titular/ nominal head of the state.

Question 2.
Vidhan Parishad (Legislative Council) is a permanent House.
Answer:

1. All members of the Vidhan Parishad (MLCs) do not retire at the same time.
2. A specific number (1/3rd) of the members retire every 2 years.
3. These vacant seats are filled again by conducting fresh elections for those seats.
4. The tenure of each member is 6 years.
5. Since the Vidhan Parishad is never fully dissolved, it is a permanent House.

Question 3.
India has 29 constituent states, but 31 Vidhan Sabha.
Answer:

1. According to the Constitution, every constituent state must have a Vidhan Sabha (Legislative Assembly).
2. India has 29 constituent states and each state has its Vidhan Sabha.
3. Out of the 7 Union Territories in India, Delhi and Puducherry have Vidhan Sabha. Hence, India has 29 constituent states, but 31 Vidhan Sabha.

Question 4.
The Chief Minister’s post is most important in the state.
Answer:

1. The Chief Minister can select his Council of Ministers according to his choice.
2. He can ask any of his ministers to resign.
3. Framing policies of public welfare and developing the state in a progressive manner entirely depends upon the Chief Minister.
4. The Chief Minister leads the state and people look at him as a problem solver.
5. His intervention in solving the problems of the state comforts the people.

Hence, all these executive powers makes the Chief Minister’s post most important in the State.

Answer the following in brief:

Question 1.
Mention the eligibility conditions for contesting Vidhan Sabha elections.
Answer:
Following are the eligibility conditions for candidates contesting for Vidhan Sabha elections:

1. He/She should be a citizen of India.
2. He/She should have completed 25 years of age.
3. He/She should be a resident of Maharashtra.

Question 2.
Do you consider Maharashtra to be progressive state?
Answer:

1. Industrial development has taken place in Maharashtra on a large scale. It has many industries based on modern technology.
2. Maharashtra’s literacy rate is higher than many other states.
3. It has a rich tradition of saints and social reformers who have nurtured progressive thinking among people.
4. Maharashtra is leading in many fields like education, health, agriculture, sports, tourism, etc.
5. Maharashtra has been a land of Movements. Many important movements like the Labour movement, Farmer’s movement have been initiated here.
6. Similarly, many progressive laws have been passed in Maharashtra.
7. Maharashtra is facing many challenges like terrorism, poverty, crime, Naxalite movements, etc. Even then, I feel that Maharashtra is a progressive state.

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 3 Force and Pressure Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 3 Force and Pressure

Class 8 Science Chapter 3 Force and Pressure Textbook Questions and Answers

1. Write proper word In the blank space:

Question a.
The SI unit of force is the ………..
(dyne, newton, joule)
Answer:
The SI unit of force is the newton.

Question b.
The air pressure on our body is equal to the …………. pressure.
(atmospheric, sea bottom, space)
Answer:
The air pressure on our body is equal to the atmospheric pressure.

Question c.
For a given object, the buoyant force in liquids of different ………… is ………….. .
(the same, density, different, area)
Answer:
For a given object, the buoyant force in liquids of different density is the same.

Question d.
The SI unit of pressure is ………………
(N/m³, N/m², kg/m², Pa/m²)
Answer:
The SI unit of pressure is N/m².

2. Make a match.

Question a.

Answer:

3. Answer the following questions in brief. 

Question a.
A plastic cube is released in water. Will it sink or come to the surface of water?
Answer:
It will come to the surface of water.
[Note: This is because its density is less than that of water. When it floats, the unbalanced force acting on it is zero.]

Question b.
Why do the load carrying heavy vehicles have large number of wheels?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The greater the surface area, the less is the pressure produced. Load carrying heavy vehicles have large number of wheels so that the load (weight, force) is distributed over large surface area of the wheels in contact with the road. Hence, the pressure decreases and the tyres do not burst.

Try this :
Pressure of a liquid:

Activity 1:
Take a plastic bottle. Take a 10 cm long piece of a glass tube on which a rubber balloon can be fitted. Warm up one end of the glass tube and gently push it into the bottle at about balloon inflates. What is observed? The pressure of water acts on the side of the bottle as well.

[Note: Here, the area of cross section of the tube remains the same. As the level of the water in the bottle rises, the mass of the water increases resulting in increase in the weight. As the applied force increases, the pressure increases. Therefore, the balloon increases in size.]

Activity 2:
Take a plastic bottle. Pierce it with a thick needle (or with a hot nail) at the points 1, 2, 3 as shown in the Fig. Fill water in the bottle up to full height. A shown in the figure, water jets will be seen emerging and projecting out. The water jet emerging from the hole at the top will fall closest to the bottle. The jet from the lowest hole falls farthest from the bottle.

Also, jets coming out from the two holes at the same level fall at the same distance from the bottle. What is understood from this? At any one level, the liquid pressure is the same. Also, the pressure increases as the depth of the liquid increases.

Question c.
How much pressure do we carry on our heads? Why don’t we feel it?
Answer:
The air pressure at the sea level is about 101 × 10³ Pa. This is the pressure that we carry on our heads. The cavities in our body are filled with air, and arteries and veins are filled with blood. Their pressure balances the pressure due to the atmosphere. Hence, we don’t feel the atmospheric pressure.

4. Why does it happen?

Question a.
Why does it happen? A ship dips to a larger depth in freshwater as compared to marine water.
Answer:
The buoyant force acting on a body is proportional to the density of the fluid in which the body is immersed. The density of freshwater is less than that of marine water. Hence, the buoyant force on a body in freshwater is less than that in marine water. Therefore, a ship dips to a larger depth in freshwater as compared to marine water.

Question b.
Why does it happen? Fruits can easily he cut with a sharp knife.
Answer:

1. It is easy to cut vegetables. fruits with a sharp knife. A blunt knife does not work here.
2. The force exerted perpendicularly on a unit area is called ‘pressure’
   
3. Presently we are considering only the force acting on an area in a direction perpendicular to it.

Question c.
Why does it happen? The wall of a dam is broad at its base.
Answer:
1. The pressure at a point in a liquid is proportional to the height of the liquid column above it. Hence, the pressure of water in a dam is much greater at the bottom of the dam than at the top.
2. To withstand this high pressure, the wall of a dam is made stronger and thicker (broad) at the base than at the top.

Question d.
Why does it happen? If a stationary bus suddenly speeds up, passengers are thrown in the backward direction.
Answer:
1. When passengers sit or stand in a stationary bus, they are in a state of rest. When the bus suddenly speeds up, the lower (parts of their body in contact with the bus acquire the speed of the bus.
2. The upper parts of their body, however, continue to be in the state of rest due to inertia. Hence, they are thrown in the backward direction.

5. Complete the following tables. 

Question a.

Answer:
Using the formula,
density = mass/volume:

Question b.

Answer:
Using the formula, relative density = density of a metal/density of water:

Question c.

Answer:
Using the formula, pressure = weight/area:

6. The density of a metal is 10.8 × 10³ kg/m³. Find the relative density of the metal.

Question a.
The density of a metal is 10.8 × 10³ kg/m³. Find the relative density of the metal.
Solution:
Data: Density of the metal = 10.8 × 10³ kg/m³
density of water = 10³ kg/m³
relative density of the metal = ?

The relative density of the metal = 10.8.

7. The volume of an object is 20 cm³ and the mass is 50 g. The density of water is 1 gm^-3. Will the object float on water or sink in water?

Question a.
The volume of an object is 20 cm³ and the mass is 50 g. The density of water is 1 gm^-3. Will the object float on water or sink in water?
Solution :

It is greater than the density of water.
Hence, the object will sink in water.

8. The volume of a plastic-covered sealed box is 350 cm³ and the box has a mass 500 g. Will the box float on water or sink in water? What will be the mass of water displaced by the box?

Question a.
The volume of a plastic-covered sealed box is 350 cm³ and the box has a mass 500 g. Will the box float on water or sink in water? What will be the mass of water displaced by the box?
Solution:

It is greater than that of water.
Hence, the box will sink in water.
The volume of water displaced by the box (V) = the volume of the box = 350 cm³

∴ The mass of water displaced by the box = 1 g.cm^-3 × 350 cm³ = 350 g.

Project:

Question a.
Video record all the experiments (Try it) in this chapter with the help of mobile phone and send to others.

Class 8 Science Chapter 3 Force and Pressure Additional Important Questions and Answers

1. Rewrite the sentences after filling the blanks

Question 1.
The tendency of an object to remain in its existing state is called its …………. .
Answer:
The tendency of an object to remain in its existing state is called its inertia.

Question 2.
Pressure = ……………
Answer:

Question 3.
1 bar = ……………….. N/m².
Answer:
1 bar = 10⁵ N/m².

Question 4.
1 atmosphere = ………….. Pa.
Answer:
1 atmosphere = 101 × 10³ Pa.

Question 5.
The SI unit of density is …………. .
Answer:
The SI unit of density is kg/m³

Write proper word In the blank space:

Question 1.
According to Archimedes’ principle, the magnitude of the force of buoyancy acting on a body is …………. .
(Vρg, Vρ/g, Vρm, mρg)
Answer:
According to Archimedes’ principle, the magnitude of the force of buoyancy acting on a body is Vρg.

Question 2.
The pascal is the unit of ……………. .
(velocity, pressure, mass, force)
Answer:
The pascal is the unit of pressure.

Question 3.
Keeping the surface area constant, if the applied force is doubled, the pressure …………….. .
(becomes double, remains the same, becomes four times, becomes half)
Answer:
Keeping the surface area constant, if the applied force is doubled, the pressure becomes double.

State whether the following statements are True or False:

Question 1.
The density of water is 1000 g/cm³.
Answer:
False. [The density of water is 1000 kg/m³ (or 1 g/cm³)]

Question 2.
Force and weight have the same units.
Answer:
True.

Question 3.
Atmospheric pressure at sea level is about 10⁶ dynes/cm².
Answer:
True.

Question 4.
The buoyant force due to a liquid is proportional to the acceleration due to gravity.
Answer:
True.

Question 5.
Atmospheric pressure increases with altitude.
Answer:
False. (Atmospheric pressure decreases with altitude.)

Question 6.
Pressure due to a given force is directly proportional to the area on which the force acts.
Answer:
False. (Pressure due to a given force is inversely proportional to the area on which the force acts.)

Question 7.
When a body is completely immersed in a liquid, the buoyant force acting on it due to the liquid is proportional to the volume of the liquid displaced by the body.
Answer:
True.

Question 8.
The density of a material is useful to determine its purity.
Answer:
True.

Question 9.
One tends to slip over a banana peel on the street and one can slip due to mud are events that occur due to reduced friction.
Answer:
True.

Question 10.
Frictional force is electromagnetic in origin.
Answer:
True.

Identify the odd term:

Question 1.
Density, Pressure exerted by a gas, Mass, Force.
Answer:
Force. (Force is a vector quantity; other quantities are scalar quantities.)

Question 2.
Lactometer, Hydrometer, Voltmeter, Submarine.
Answer:
Voltmeter. (Its working is not based on Archimedes’ principle. The working of a lactometer, hydrometer and submarine is based on Archimedes’ principle.)

Rewrite the following table in such a way that Column 2 and Column 3 will match with Column 1:

Question 1.

Answer:

Answer the following questions in one sentence:

Question 1.
Which of the following has more inertia? A ₹ 10 coin and a ₹ 1 coin.
Answer:
A ₹ 10 coin has more inertia than a ₹ 1 coin.

Question 2.
Name the physical quantity expressed in pascal.
Answer:
Pressure is expressed in pascal.

Question 3.
State the SI unit of pressure.
Answer:
The SI unit of pressure is N/m², also called the pascal.

Question 4.
Name the property of a liquid due to which it exerts an upward force on an object immersed in it.
Answer:
Buoyancy is the property of a liquid due to which it exerts an upward force on an object immersed in it.

Question 5.
Name the principle used in designing ships and submarines.
Answer:
Archimedes’ principle is used in designing ships and submarines.

Question 6.
What is specific gravity?
Answer:
The specific gravity of a substance is another name used for relative density, i. e., the ratio of the density of the substance to the density of water.

Question 7.
State any one factor on which the pressure exerted by a liquid at a point inside the liquid depends.
Answer:
The pressure exerted by a liquid at a point inside the liquid depends on the density of the liquid.

Question 8.
State any one factor on which the buoyant force due to a liquid depends.
Answer:
The buoyant force due to a liquid depends on the density of the liquid.

Question 9.
Name the device used to determine the purity of a sample of milk.
Answer:
The lactometer is used to determine the purity of a sample of milk.

Question 10.
Name the device used to determine the density of a liquid.
Answer:
The hydrometer is used to determine the density of a liquid.

Question 11.
Name two instruments whose working is based on Archimedes’ principle.
Answer:
Working of the lactometer and hydrometer is based on Archimedes’ principle.

Answer the following questions:

Question 1.
Give three examples to show that a force acts on two bodies through an interaction between them.
Answer:

1. Consider a car at rest on a level (plane) road. If it is pushed from behind, it moves in the forward direction.
2. Iron nails get attracted to the poles of a magnet and stick to the magnet.
3. The moon revolves around the earth.

Question 2.
What is a contact force? Give one example.
Answer:
A force that acts through a direct contact of two objects or via one more object, is called a contact force.
Example: If a ball at rest on the ground is kicked, it starts moving.

Question 3.
What is a non contact force? Give one example.
Answer:
A force that acts between two objects even if the two objects are not in contact, is called a non contact force.
Example: The earth revolves around the Sun.

Use your brainpower!
Make a list of some more examples in which contact and non contact forces are applied. Write the types of force.
Answer:
1. Some examples in which contact forces are applied:

• to cut an apple with a knife (muscular force, frictional force)
• to lift a ball lying on the ground (muscular force, frictional force)

2. Some examples in which non contact forces are applied:

• the motion of the earth around the Sun (gravitational force)
• the motion of an electron around the nucleus of an atom (mainly the electric force).

Question 4.
In the following examples, state whether the force is a contact force or non contact force:

1. a reluctant dog is being pulled by his master
2. a boy playing football is kicking the ball away
3. when iron nails are brought near a magnet, they are attracted to the poles of the magnet and stick to the magnet
4. a coconut is falling from the coconut tree
5. when a comb is rubbed against hair, small pieces of paper kept on a table get attracted to the comb
6. when brakes are applied to a moving bicycle, it stops after some time

Answer:

1. contact force
2. contact force
3. non contact force
4. non contact force
5. non contact force
6. contact force.

Question 5.
Give one example in which frictional force is useful.
Answer:
While walking, we push the ground behind with our feet. In the absence of friction between the ground and the lower surface of our feet, we will slip and will not be able to walk.
[Note: Frictional force is electromagnetic in origin.]

Try this: 
Take two plastic bottles with rectangular shape. Close their openings by fitting the lids tightly. Keep two small bar magnets on them and fix them neatly using a sticking tape.

Fill a big plastic tray with water and leave the two bottles floating with magnets at the top. Take one bottle near the other. If the north pole of the magnet is near the south pole of the other magnet, the bottles will head towards each other, because unlike poles attract each other.

Observe what will happen when the directions of the bottles are changed. We can observe change in the motion of the bottles without any direct contact. This means that there exists a non contact force between the two magnets.

Observation: When the directions of the bottles are changed, if the north pole of one magnet is near the north pole of the other magnet (or the south pole of one magnet is near the south pole of the other magnet), the bottles will move away from each other because like poles repel each other.

Use your brain power!

Question.
You have learnt about static electricity in the previous standard. Electrostatic force is a non contact force. To verify this, which experiment will you perform?
Answer:

Do not switch on the fan in the room. Keep very small pieces of paper on the table. Rub a plastic comb against hair and bring it near the bits of paper. You will find that the bits of paper are attracted by the comb. The comb, on rubbing acquires electrostatic charge. It induces opposite charges on the bits of paper. Hence, the bits of paper are attracted by the comb.

Try this: 
Balanced forces and unbalanced force:

Take a cardboard box, tie thick string to its two sides and keep it on a smooth table as shown in Fig. Take the strings on both sides of the table. Tie weighing pans to the two ends. Keep equal masses in both the pans. The box does not move on the table.

If more mass is kept in one of the pans than in the other, the box starts moving in the direction of that pan. Equal gravitational force acts on both the pans when equal masses are kept in them. This means balanced forces act on the box, with effective force equal to zero as these are acting in opposite directions.

On the contrary, if more mass is kept in one pan than in the other, the box starts moving in the direction of the pan with more mass. When unequal forces are applied to the box on the two sides, an unbalanced force acts on the box resulting in imparting motion to the box.

Children playing tug of war pull the rope in their respective directions. If the pull of the force is equal on the two sides, the rope does not move. If the force is more on one side, the rope moves in that direction. This means that initially, the two forces are balanced; the rope moves in the direction of higher force when the forces become unbalanced.

Let us see one more example. When a big grain storage container is required to slide on the ground, it becomes easier if two persons push it rather than one person. When the force is applied by both in the same direction, the movement is easy. You may have experienced this. What do we understand from this example?

1. If several forces are applied on an object in the same direction, a force equal to their addition acts on that object.
2. If two forces are applied on one object in directions opposite to each other, a force equal to their difference acts on the object.
3. A force is expressed in magnitude and direction.

Force is a vector quantity. If more than one force are acting on a body, then the effect on the body is due to the net force. When a force is applied on a stationary object it moves, its speed and direction change. Similarly, a force is required to stop an object in motion.

An object can change its shape due to force. While kneading a dough made from flour, the dough changes its shape when a force is applied. A potter applies a force in a specific direction while shaping the pot. Rubber, when stretched, expands. There are many such examples. ,

Question 6.
What are balanced forces?
Answer:
If a body is acted upon by two forces, equal in magnitude, opposite in direction and having the same line of action, the forces are called balanced forces. Here, the net force acting on the body is zero.

Question 7.
What is an unbalanced force?
Answer:
If two or more forces act on a body such that their resultant is not zero, the resultant is an unbalanced force.
[Note: Unbalanced force acting on a body = mass of the body × acceleration of the body.]

Question 8.
Explain: Force has magnitude as well as direction. OR Force is a vector quantity.
Answer:
The effect of force applied to a body depends upon how much force we supply, i.e., the magnitude of the force, and the direction in which the force is applied. Consider a ball at rest on the ground. When ; we push it, it starts rolling. The greater the applied force, the greater is the speed acquired by the ball.

Consider a body moving in a straight line, If we apply a force in the direction of motion of the body, the speed of the body increases. On the contrary, if we apply a force in the direction opposite to that of motion of the body, the speed of the body decreases. These ( examples show that force has magnitude as well as direction, i.e., force is a vector quantity.

Question 9.
Explain the term balanced forces.
Answer:
Consider a rigid body acted upon by two forces, equal in magnitude, opposite in . direction and having the same line of action. These forces are called balanced forces as their net effect on the body is zero.
Example: A glass slab kept on a table is acted upon by two balanced forces: (i) the weight of the slab acting downward and (ii) the upward force on the slab due to the table. Their net effect on the slab being zero, the slab remains at rest.

Question 10.
Explain the term unbalanced force.
Answer:
A single force acting on a body is an unbalanced force. It produces acceleration in the body. If two or more forces act on a body such that their resultant is not zero, the resultant is an unbalanced force responsible for accelerating the body.
Example: When a ball lying on the ground is hit with a bat, the ball is set in motion by the applied force.

Question 11.
What will happen if the force is removed completely when an object acquires a certain speed?
Answer:
If the force is removed completely when an object acquires a certain speed, the object will move with the velocity it has at the instant the force is removed.

For example, a body moving with constant speed along a circular path in a horizontal plane will fly tangentially in the sense of motion if the centripetal force (the force directed towards the centre of the circle) is removed completely.

Always remember:

1. The tendency of an object to remain in its existing state is called its inertia.
2. This is why an object in stationary state remains in the same state and an object in motion remain in the state of motion in the absence of an external force.

Types of inertia:

1. Inertia of the state of rest: An object in the state of rest cannot change its state of rest due to its inherent property. This property is called the inertia of the state of rest.

2. Inertia of motion: The inherent property of an object due to which its state of motion cannot change, is called its inertia of motion. For example, a revolving’ electric fan continues to revolve even after it is switched off, passengers sitting in the running bus get aerk in the forward direction if the bus suddenly stops.

3. Directional inertia: The inherent property of an object due to which the object cannot change the direction of its motion, is called directional inertia. For example, if a vehicle in motion along a straight line suddenly turns, the passengers sitting in it are thrown opposite to the direction of turning.

Try this:
Activity 1:
Take a postcard and keep it on a glass. Keep a 5 Rupee coin on it. Now skilfully push the card. The coin straight away falls in the glass. Have you ever done this?
Answer:
Yes. (Explanation: The postcard moves forward due to the applied force and then falls due to the earth’s gravitational force. In the absence of adequate frictional force between the coin and the postcard, the coin does not move forward with the postcard, but straightaway falls in the glass due to the earth’s gravitational force.)

Activity 2: Hang a half a kg mass from a stand, with a string 1. Tie another string 2 to the mass and keep it hanging. Now pull the string 2 with a jerk. The string 2 breaks but the mass does not fall. Heavy mass does not move. Now pull the string 2 slowly. The string 1 breaks and the mass fall down. This is because of the tension developed in the string 2 due to the mass.

(Explanation: (1) As no force acts on the mass, it remains at rest due to inertia. (2) The transmission of force results in the tension in the string 1. As the string 1 cannot withstand it, it breaks and the mass falls down.)

Question 12.
What are the three types of inertia?
Answer:
Types of inertia:

• inertia of rest
• inertia of motion
• inertia of direction.

Question 13.
What is inertia of rest ? Give two examples of inertia of rest.
Answer:
The inherent property of a body by virtue of which it cannot change its state of rest is called the inertia of rest.
Examples:

1. When we dust a carpet, the carpet moves but the dust particles in it remain at rest due to inertia and hence get separated from the carpet. Hence, the carpet becomes clean.
2. When a bus starts suddenly, the passengers experience a backwarderk due to inertia.

Question 14.
What is inertia of motion? Give two examples of inertia of motion.
Answer:
The inherent property of a body by virtue of which it cannot change its state of motion is called the inertia of motion.
Examples:

1. When a fan is switched off, its blades continue to rotate for some time. Due to internal friction and friction with air, the blades of the fan stop rotating after some time.
2. Passengers in a bus experience a forwarderk when the bus stops suddenly due to application of brakes.

Question 15.
What is inertia of direction? Give two examples of inertia of direction.
Answer:
The inherent property of a body by virtue of which it cannot change its direction of motion is called the inertia of direction.
Examples:

1. While sharpening a knife, sparks fly off tangentially in the sense of motion from the grinding stone.
2. When a vehicle moves, the mud particles sticking to its wheels fly off tangentially in the sense of motion. Hence, mudguards are fitted to vehicles.

Question 16.
Why do we fall sideways when we are sitting in a bus and it takes a sharp turn?
Answer:
When we sit in a bus and the bus is in motion, we are in a state of motion in the same direction. When the bus takes a sharp turn, our body tends to maintain the state of motion in the straight line due to inertia. The portion of our body in firm contact with the seat acquires the motion along the curved path, but the upper portion of our body, tends to move in the initial direction of motion. Hence, we fall sideways.

Question 17.
What happens when you shake a wet piece of cloth? Explain your observation.
Answer:

1. When we shake a wet piece of cloth, water droplets come out.
2. Initially, the wet piece of cloth is at rest. When the cloth is shaken, it is accelerated, but the water droplets in it, due to inertia, tend to maintain the state of rest. Hence, the droplets come out.

Question 18.
If brakes are suddenly applied to a moving car, the passengers in the car are pushed in the forward direction. Explain why.
Answer:
1. The passengers in a moving car have the same velocity as that of the car. When brakes are suddenly applied to the car, it stops suddenly and the lower parts of the passengers’ bodies in contact with the seats, come to rest.

2. The upper parts of their bodies, however, continue to be in a state of motion due to inertia. Hence, the passengers are pushed in the forward direction.

Question 19.
A person alighting from a moving train is likely to fall in the direction of motion of the train. Explain why.
Answer:

1. A person in a moving train has the same velocity as that of the train. After alighting from the moving train his feet come to rest on the platform.
2. However, due to inertia, the upper part of his body continues to be in a state of motion in the direction of motion of the train. Hence, he is likely to fall in the direction of motion of the train.

Try this: 

Activity 3: Take some sharp pointed nails and push them into a wooden plank by hammering on their heads. Now take? a nail and hold it with its head on the plank and hammer it down from the pointed end. When pressing the drawing pins into a drawing board, they get into the board easily. By applying a force using the thumb one can push the pins into the boards. On the contrary, while pressing ordinary pins into the board with a thumb, the thumb may get hurt.

What does this simple experiment tell?
The nail easily penetrates into wood from its pointed end. From this you will notice that when a force is applied on the head of the nail, it is easy to hammer it into the plank.
Explanation: The less the area of the surface on which the force is applied, the greater is the effect of the force.

Question 20.
Define pressure.
Answer:
The force exerted perpendicularly on a unit area is called pressure.

Use your brain power!

Question 1.
It is easy to cut vegetables, fruits with a sharp knife. A blunt knife does not work here. Why does this happen?
Answer:
The effect of a given force varies l inversely as the area of the surface on ( which the force is applied. The less the surface area, the greater is the effect of the force. The cutting edge of a sharp ’ knife has less cross sectional area relative to that of a blunt knife. Hence, it is easy to cut vegetables, fruits with a sharp knife, rather than with a blunt knife. For a given force, pressure is inversely proportional to the area of the surface on which the force acts.

Question 21.
State the formula for pressure, Hence, determine the unit of pressure.
Answer:

The SI unit of force is the newton (N) and that of area is m². Therefore, the SI unit of pressure is N/m². It is called the pascal (Pa). 1 Pa = 1 N/m².
[Note: The unit pascal is named in honour of Blaise Pascal (1623-62), French mathematician, physicist and philosopher.]

Question 22.
State the CGS unit of pressure. State the relation betweeen the SI and CGS units of pressure.
Answer:
The CGS unit of pressure is the dyne/cm².
IN = 105 dynes, 1m² = (102 cm)² = 104 cm² 1 Pa = 1 N/m² = 105 dynes/104 cm² = 10 dynes/cm².

Question 23.
State the factors on which pressure depends.
Answer:
Pressure depends on the applied force and the area of the surface on which the force is applied.

Question 24.
Explain with a suitable example that pressure varies inversely as the area of the surface on which the force is applied, if the force remains constant.
Answer:
The tip of a pointed nail has an extremely small area, while that of a blunt nail has a comparatively large area. A given force creates a large pressure on the pointed nail and it can be easily hammered into the wood, while a very less pressure is created on the blunt nail and it cannot be easily hammered into the wood.

This shows that pressure varies inversely as the area of the surface on which the force is applied, if the force remains constant. If the same force is applied to surfaces having different areas, the pressure is more on the surface having a smaller area.

[Note: The bottom surface of a camel’s feet is broad. Hence, the camel’s weight acts on a large surface area. This reduces the pressure on the sand. Hence, the camel’s feet do not penetrate deep into the sand. Therefore, it becomes easier for the camel to walk on sand.]

Question 25.
With neat diagrams, describe an experiment to show that pressure increases if the surface area is decreased, keeping the applied force the same.
Answer:
Take a brick measuring 20 cm x 10 cm x 5 cm. Take some clay in a glass trough. Add water to it and knead it into a soft dough. Place the brick on the dough with one of its faces measuring 20 cm x 10 cm in contact with the dough. Observe how deep the brick penetrates into the dough.

Clean the brick and place it on the dough with one of its faces measuring 10 cm x 5 cm in contact with the dough. Observe how deep the brick penetrates into the dough. You will find that the brick penetrates deeper in this case than that in the first case.

• In the first case, the weight of the brick acts on a surface area of 200 cm².
• In the second case, the weight of the brick acts on a surface area of 50 cm².
• This shows that pressure increases if the surface area is decreased, keeping the applied force the same.

Question 26.
State the unit for pressure used in atmospheric science. How is it related to the unit pascal?
Answer:
In atmospheric science, the unit used for pressure is the bar. 1 bar = 10 Pa (pascal).

Try this:

Question 1.
Do the activity as depicted in Figure What is seen?
Answer:
In Fig.(a), the plank is horizontal. In Fig.(b), four books are placed side by side on the plank. The plank bends slightly due to the pressure produced by the weight of the books.

In Fig.(c), the four books are placed one above the other in the middle of the plank. Here the area of the surface of the plank on which the force acts is reduced by a factor of four relative to the earlier case. Hence, the plank bends considerably.
[Note: This shows that for a given force, pressure varies inversely as the area of the surface on which the force acts.]

Use your brainpower! 

Question 1.
You must have seen a vegetable vendor carrying a basket on her head. She keeps a twisted piece of cloth on the head, below the basket. How does it help?
Answer:
Keeping a twisted piece of cloth on the head increases the area of the surface on which the weight of the basket containing vegetables acts. Hence, the pressure produced by the force (weight) is reduced and it becomes easier to carry the basket.

Question 2.
We cannot stand at one place for a long time. How then can we sleep on a place for 8 and odd hours?
Answer:
When we stand, our weight acts on relatively small surface area, resulting in increased tension on the muscles of our legs. Hence, we cannot stand at one place for a long time. When we sleep, our weight acts on relatively large surface area, resulting in comparatively reduced tension. Therefore, we can sleep on a place for 8 and odd hours.

Question 3.
For skiing on ice, why are long flat skis used?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The greater the surface area, the less is the pressure produced. The skis used to slide over snow are long and flat so that the area is increased and hence the pressure is decreased. This makes it easier to slide over snow.

Question 27.
Why do the blades of a pair of scissors have sharp edges?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The less the surface! area, the greater is the pressure produced, The blades of a pair of scissors have sharp edges so that the area is decreased and hence the pressure is increased. This makes cutting • an object such as cloth easier.
[Note: Answers to questions such as why is the blade of an axe sharp? or why is the blade of a saw sharp? can be written on the basis of the answer given above.]

Question 28.
Why does a needle have s sharp point?
Answer:
The pressure produced by a given force depends on the areas of the surface on which the force acts. The less the surface area, the greater is the pressure produced. A needle has a sharp point so that the area is decreased and hence the pressure is increased. This makes the action of piercing easier.

Question 29.
Why do school bags have broad shoulder straps?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The greater the surface area, the less is the pressure produced. School bags have broad shoulder straps so that the weight of the bag is distributed over a large surface area thereby decreasing the pressure on the shoulders of the student carrying the bag.

Question 30.
How will the pressure change if the area is doubled keeping the force the same?
Answer:
If the area is doubled, keeping the force the same, the pressure will become half the initial pressure.

Question 31.
How will the pressure change if the force is doubled, keeping the area the same?
Answer:
If the force is doubled, keeping the area the same, the pressure will become double the initial pressure.

Question 32.
State the characteristics of the pressure due to a liquid (or a fluid in general).
OR
Write a short note on the pressure due to a liquid (a fluid in general).
Answer:
Characteristics of the pressure due to a liquid (or a fluid):

1. The pressure at a point in a liquid (or a fluid) is due to the weight of the liquid (fluid) column above that point.
2. It acts on all sides of the container.
3. At a given depth it is the same in all directions.
4. It is independent of the size and shape of the container.
5. It is proportional to the height of the liquid (fluid) column above the given point.
6. It is proportional to the density of the liquid (fluid).
7. It is proportional to the acceleration due to gravity at the given place.

[Note: The pressure exerted by a liquid (or gas or fluid) at a depth h below the free surface of the liquid = hpg, where p is the density of the liquid (or gas or fluid) and g is the acceleration due to gravity.]

Question 33.
Give two examples to show that air exerts equal pressure in all directions.
Answer:

1. When air is filled in a balloon, it acquires its characteristic shape such as round or oval.
2. When a bicycle tube is filled with air, it acquires its characteristic (tube-like) shape throughout. This shows that air exerts equal pressure in all directions.

Question 34.
Whatisafluid?Givetwoeamples.
Answer:
A fluid is a substance which can flow.
Examples:

1. Water (liquid)
2. Air (gas)

[Note: Liquids and gases together are called fluids. Gases have very low viscosity compared to liquids. A liquid with low viscosity flows easily. A liquid with high viscosity does not flow easily.]

Question 35.
Take two rubber balloons. Fill one with water and blow air into the other. Now prick both balloons with a pin. What do you observe?
Answer:
Water and air both come out of the balloons. Air escapes quickly compared to water and produces a loud sound.

Question 36.
State the characteristics of pressure exerted by a fluid.
OR
Write a short note on pressure exerted by a fluid.
Answer:
Characteristics of pressure exerted by a fluid:

1. A fluid due to its weight, exerts pressure on the base as well as the walls of the container that holds it.
2. A fluid exerts pressure on a body immersed in it.
3. The pressure exerted on any confined mass of fluid is transmitted undiminished in all directions.

[Note: The pressure exerted by a fluid is a scalar quantity.]

Question 37.
Take an empty can. Pour small quantity of water in it. Boil this water for a few minutes until the steam has driven out most of the air. Now close the can with the stopper tightly. Allow it to cool by pouring cold water over it. What do you observe?
Answer:
The can gets gradually crushed.
[Note: The steam inside the can condenses to form water as the can cools. Therefore, the pressure inside the can becomes much less than the external pressure of the air. Hence, the can gets crushed.]

Question 38.
Put a folded newspaper on a plastic bag. Blow air into the bag. What do you observe?
Answer:
The plastic bag inflates as air is blown into it. This raises the folded news¬paper put on the bag.

Question 39.
What is meant by atmospheric pressure?
Answer:
The earth is surrounded by air from all sides. This layer of air is called the atmosphere. Its density is high up to about 16 km from the earth’s surface. Beyond that, up to about 400 km, its density is very low. Air, due to its weight, exerts pressure on the surface of the earth.

The pressure exerted by air or the atmosphere surrounding the earth is known as the atmospheric pressure. It is the ratio of the weight of the air to the area of the surface of the earth. It decreases with altitude as the density of air decreases with altitude and also the weight of the air column above a given place.
[Note: At sea level the atmospheric pressure is about 105 Pa. We do not feel it because the pressure of blood and other fluids in our body balances it.]

Question 40.
State the relation between 1 atmosphere and the pascal.
Answer:
1 atmosphere = (about) 101 × 10³ Pa (pascal)
[Note: The air pressure at the sea level is (about) 1 atmosphere.
1 atmosphere = 101325 Pa.
1 bar = 10³ mbar (millibar)
1 mbar w 10³ Pa (hectopascal)
Atmospheric pressure is expressed in mbar or hectopascal (hPa).]

Use your brain power!

Question 1.
At the sea level the atmospheric pressure 101 × 10³ Pa is acting on a table top of size 1 m². Under such a heavy pressure, why doesn’t the table top crumble down?
Answer:
The air below the table top exerts pressure 101 × 10³ Pa on it in the upward direction. Hence, the table top doesn’t crumble down.

Question 41.
Think – Why?
Question i.
Some people feel their ears popping at the top of a mountain.
Answer:
Atmospheric pressure decreases with altitude. At the top of a mountain, it becomes less than the internal pressure in the ear. Hence, some people feel their ears popping at the top of a mountain.

Question ii.
Some people feel breathless as they climb higher and higher on a mountain.
Answer:
Atmospheric pressure decreases with altitude. Hence, some people feel breathless as they climb higher and higher on a mountain.

Question iii.
We can enjoy a cold-drink or fruit juice with the help of a straw but can we imagine drinking a cold-drink or fruit juice on the moon using a straw?
Answer:
When we suck air in the straw, the pressure of the air in the straw becomes less than that of the outside air on the cold drink or fruit juice in the bottle (or the glass). Hence, the cold drink or fruit juice rises in the straw and enters our mouth. We can then drink it. There is no atmosphere on the moon. Hence, it is not possible to enjoy a cold drink or fruituice on the moon by using a straw.

Question iv.
People are often advised not to carry fountain pens while travelling by air.
Answer:
The ink in a fountain pen (filled at sea level at atmosphere pressure) may come out through its mouth while travelling by air if the outside pressure becomes less than the pressure in the ink holder of the pen. This can spoil the clothes/purse/bag. Hence, people are often advised not to carry fountain pens while travelling by air.

Question 42.
Why do some people have earache when they travel by an aeroplane?
Answer:
When an aeroplane descends at a high speed, there is an increase in air pressure. This increases the pressure on the ear drum. Hence, some people have earache when they travel by an aeroplane.

Question 43.
Explain why a person may bleed from the nose when at a great height above the sea level.
Answer:
The pressure exerted by the blood in blood capillaries is slightly more than the atmospheric pressure and acts in a direction opposite to that of the atmospheric pressure. Atmospheric pressure decreases with height and at a great height above the sea level, it is very low.

As a result, there arises a difference in the internal and external pressures on the walls of the cells and blood capillaries. If the difference is large, it may cause the cell wall and the blood capillaries to burst. Thus, the capillaries in the nose (and ear) may burst causing bleeding.

Question 44.
When a rubber sucker is pressed onto a flat glass surface, it sticks tightly on the surface. Why? You need a large force to separate it from the surface. Why?
Answer:
When a rubber sucker is pressed onto a flat glass surface, practically all the air between the surfaces of the sucker and the glass is pushed out. The air pressure there becomes much less than the atmospheric pressure. Hence, the sucker sticks to the glass due to the external atmospheric pressure. The atmospheric pressure is about 105 Pa. It is very large. Hence, to work against it to separate the sucker from the glass, a large force is needed.

Question 45.
Describe a simple experiment to demonstrate atmospheric pressure.
Answer:
Fill a glass completely with water (to its brim) and cover it with a flat and stiff card paper (or a piece of glass). Holding your palm on the card, turn the glass upside down and take the palm away from the card.

You will find that the water does not spill. The atmospheric pressure on the card (acting upward) is greater than the pressure of the water in the glass (acting downward). Hence, the water in the glass does not spill.

Question 46.
Explain the working of an ink dropper.
[Application]
Answer:
An ink dropper consists of a tube of glass or plastic, with one end tapering to a narrow opening and the other end fitted with a small rubber bulb. When the narrow open end is dipped into the ink and the rubber bulb is pressed, some air in the tube escapes through the open end. This reduces the air pressure inside the dropper.

On releasing the bulb, the atmospheric pressure on the ink pushes the ink into the dropper. The dropper is then taken out and its open end is held over the open barrel of the pen. The bulb is then pressed so that the ink in the dropper enters the pen.
[Note: The medicine dropper works in the same manner.]

Question 47.
Why is the opening of a dropper very narrow?
Answer:
The pressure produced by a given force is inversely proportional to the area of the surface on which the force acts. The opening of a dropper is very narrow. Hence, its area of cross-section is very small. As a result, even if the dropper has a small amount of ink it, its pressure can equal the atmospheric pressure. As the opening is narrow, it is easier to transfer the ink to the pen. The possibility of ink spilling is very low.

Question 48.
What is the characteristic of the cap of eye drop bottles?
Answer:
The cap of an eye drop bottle is fitted with a dropper.

Question 49.
Explain the working of a syringe
used by children when they play with coloured water. [Application]
Answer:
As shown in the figure, a syringe used by children when they play with coloured water consists of a cylinder made of plastic or metal fitted with a piston. One end of the cylinder is in the form of a narrow

tube. The snugly fitting piston can slide in , and out smoothly. The rod connected to the i piston passes through a hole in the centre of the lid and has a handle at the other end. When the tip of the narrow tube is dipped in coloured water (or any other liquid) and the piston is pushed towards the tip, up to the bottom, most of the air in the cylinder escapes through the tube, reducing the pressure.

When the piston is moved up, the coloured water rises in the part of the cylinder below the piston due to the atmospheric pressure. Finally, the inner pressure equals the atmospheric pressure and no more coloured water enters in or comes out.

To spray the coloured water, the tube is taken out and the piston is moved towards the opening of the tube. As the inner pressure is now greater than the atmospheric pressure, the coloured water gushes out of the narrow opening of the tube.

Question 50.
How does the doctor’s syringe work?
Answer:
As shown in the figure, a syringe used by children when they play with coloured water consists of a cylinder made of plastic or metal fitted with a piston. One end of the cylinder is in the form of a narrow

tube. The snugly fitting piston can slide in , and out smoothly. The rod connected to the i piston passes through a hole in the centre of the lid and has a handle at the other end.

When the tip of the narrow tube is dipped in coloured water (or any other liquid) and the piston is pushed towards the tip, up to the bottom, most of the air in the cylinder escapes through the tube, reducing the pressure. When the piston is moved up, the coloured water rises in the part of the cylinder below the piston due to the atmospheric pressure.

Finally, the inner pressure equals the atmospheric pressure and no more coloured water enters in or comes out. To spray the coloured water, the tube is taken out and the piston is moved towards the opening of the tube. As the inner pressure is now greater than the atmospheric pressure, the coloured water gushes out of the narrow opening of the tube.

The tip of a syringe is fitted with a very fine and hollow needle. The required quantity of medicine can be taken in the syringe with the help of the piston. The medicine can then be injected into the body of a patient using the needle and the piston.

Question 51.
Explain the origin of pressure due to a gas enclosed in a container.
Answer:
Molecules of a gas are in a state of continuous random motion. These molecules possess energy due to motion. When the molecules collide with a wall of the container, they rebound. A large number of molecules collide with the wall every second. Hence, a significant force is exerted on the wall. Pressure is the force per unit surface area. Thus, a pressure is exerted by the gas on a wall of the container.

Try this: 

Buoyant force:
Take a plastic bottle and fix the lid tightly. Now place it in wafer and see. It will float on water. Try and push it into the water. Even when pushed, it continues to float. This experiment can also be done with a plastic hollow ball. Now fill the bottle with water to the fullest capacity and close the lid, and release in water. The bottle will float inside the water. Why does this happen?

The empty plastic bottle floats on the surface of water. On the contrary, the bottle full of water floats inside water but does not go to the bottom. The weight of the empty bottle is negligible as compared with the weight of the water inside.

Such a bottle with water neither floats on the surface, nor does it go to the bottom. This means the force due to gravity acting downwards (fg), must have been balanced by an opposing force in the upward direction (fb) on the bottle filled with water. This force must have originated from the water surrounding the bottle. The upward force acting on the object in water or other fluid or gas is called buoyant force (fg).

Question 52.
Define buoyant force.
Answer:
The upward force acting on the object in water or other fluid or gas is called the buoyant force.

Question 53.
State the factors on which the buoyant force depends.
Answer:
The buoyant force depends upon the volume of the object immersed in the fluid (V), the density of the fluid (ρ1) and the acceleration due to gravity (g) at that place.
[Note: Magnitude of the buoyant force = Vρ1 g.]

Use your brain power!

Question.
While pulling a bucket from a well, the bucket full of water immersed fully in water appears to weigh less than when it has been pulled out of water. Why?
Answer:
1. When a bucket full of water is immersed in water, the net force acting on the bucket = weight of the bucket full of water-the buoyant force exerted by the water on the bucket. The buoyant force due to a fluid is proportional to the density of the fluid.

2. The density of water is much greater than that of air. Therefore, the buoyant force acting on a bucket full of water while it is in water is much greater than that when it is out of water, i.e., in air. Hence, it appears to weigh less, while it is in water than when it has been pulled out of water.

Try this:

Question 1.
Take a piece of thin aluminum sheet and dip it in water in a bucket. What do you observe?
Answer:
It sinks in the water.

Question 2.
Now shape the same piece of aluminium into a small boat and place it on the surface of water. It floats, isn’t it?
Answer:
Yes, the boat floats on the surface of water.

Question 54.
A lemon sinks in a glass filled with water but it floats when we stir in two spoons of salt in the water. Explain why.
Answer:
When salt is dissolved in water, the density of the water increases. The buoyant force is proportional to the density of the liquid. Hence, when the lemon is immersed in the water containing salt, the magnitude
of the buoyant force acting on the lemon becomes greater than the magnitude of the weight of the lemon. Therefore, it floats in water.

Do you know?

How is it decided that an object left in a liquid will get sink in the liquid, will float on the surface, or will float inside the liquid?
1. The object floats if the buoyant force is larger than its weight.
2. The object sinks if the buoyant force is smaller than its weight.
3. The object floats inside the liquid if the buoyant force is equal to its weight. Which forces are unbalanced in the above cases?
Answer:
Unbalanced force:
1. Magnitude of the unbalanced force acting on the object = magnitude of the buoyant force on the object-magnitude of the weight of the object. The direction of the unbalanced force is the direction of the buoyant force.

2. Magnitude of the unbalanced force on the object = magnitude of the weight of the object – magnitude of the buoyant force on the object. The direction of the unbalanced force is the direction of the weight of the object.

3. Here, the unbalanced force is zero.

Try this:

Take a long rubberband and cut it at one point. At one of its ends tie a clean washed stone or a 50 g weight as shown in Figure
Now hold the other end of the rubberband and make a mark there. Keep the stone hanging in air and measure the length of the rubberband from the stone to the mark made earlier.

Now take water in a pot and hold the rubberband at such a height that the stone sinks in it. Again measure the length of the rubberband up to the mark. What is observed? This length is shorter than the earlier length. While dipping the stone in water, length of the stretched rubber gets slowly reduced and is minimum when it sinks completely. What could be the reason for a shorter length of the rubberband in water?

When the stone is sunk in water, a buoyant force acts on it in the upward direction. The weight of the stone acts downwards. Therefore, the force which acts on it in the downward direction is effectively reduced.
(This decreases the downard force on the rubberband. Hence, its length decreases.)

Question 55.
State Archimedes’ principle.
Answer:
Archimedes’ principle: When an object is partially or fully immersed in a fluid, a force of buoyancy acts on it in the upward direction. This force is equal to the weight of the fluid displaced by the object.
[Note: The two forces mentioned here are equal in magnitude and opposite in direction.]

Question 56.
Using Archimedes’ principle, determine the magnitude of the buoyant force.
Answer:
Let m = mass of the body (object) immersed in the fluid, V = volume of the body, ρ = density of the body, ρ1 = density of the fluid, g = magnitude of the acceleration due to gravity. Suppose that the body is completely immersed in the fluid. Then the volume of the fluid displaced by the body = V. According to Archimedes’ principle, magnitude of the buoyant force = magnitude of the weight of the fluid displaced by the body = mass of the displaced fluid × g = volume of the displaced fluid × density of the fluid × g
(as density = mass/volume)

If the body is partially immersed in the fluid, the volume of the fluid displaced by the immersed part of the body = xV ; here 0 < x < 1.
In this case, the magnitude of the buoyant force

Question 57.
Using the formula for the magnitude of the buoyant force, state under what conditions the body will
1. sink in the fluid
2. float in the fluid
3. remain in equilibrium anywhere within the fluid.
Answer:
Magnitude of the buoyant force on the body = mg \(\left(\frac{\rho_{1}}{\rho}\right)\)
= magnitude of the weight of the body × \(\left(\frac{\rho_{1}}{\rho}\right)\)
1. If the density of the fluid (ρ1) is less than the density of the body (ρ), the magnitude of the buoyant force on the body will be less than the magnitude of the weight of the body. Therefore, the body will sink in the fluid.|

2. If the density of the fluid is greater than that of the body, the magnitude of the buoyant force on the body will be greater than that of the weight of the body. Therefore, the body will float in the fluid.

3. If the density of the fluid is equal to that of the body, the magnitude of the buoyant force on the body will be equal to that of the weight of the body. Therefore, the body will remain in equilibrium anywhere within the fluid.

Use your brain power!

Question.
Explain the observations in the earlier experiments according to the Archimedes’ principle.
Answer:
The increase in the length of the rubberband (y) is proportional to the downward force (f) acting on it.
1. When the stone tied to the rubberband is hanging in air, the magnitude of the buoyant force exerted by air on the stone is negligible compared to that of the weight of the stone. Hence, ignoring it, we have f = fg = mg, where m is the mass of the stone and g is the acceleration due to gravity.

2. When the stone is immersed partially in water, f = fg – fb, where fb is the magnitude of the buoyant force exerted by water on the stone.
Now, fg = Vρg and fb = xVρwg, where V = volume of the stone, ρ = density of the stone, xV= volume of the water displaced by the part of the stone immersed in water = volume of the part of the stone immersed in water (x < 1) and ρ = density of water.

This shows that as the stone is gradually lowered in water, x goes on increasing and hence/goes on decreasing. Therefore, elongation (y) of the rubberband goes on decreasing, i.e., the length of the rubberband goes on decreasing.

3. When the stone is completely immersed in water, x becomes maximum, equal to 1. Here, f = fg \(\left(1-\frac{\rho_{\mathrm{W}}}{\rho}\right)\). This is the minimum value of. Here, the elongation of the rubberband is minimum, i.e., the length of the rubberband is minimum.

Question 58.
State the applications of Archimedes’ principle.
Answer:
Archimedes’ principle is used in the construction of ships and submarines. The working of the lactometer and hydrometer is based on Archimedes’ principle.
[Note: The hydrometer is used to determine the density or relative density of a liquid.]

Question 59.
If a spring balance is used to weigh a body, will the weight of the body be the same in vacuum and air? Explain why.
Answer:
When a body is suspended in air, the buoyant force acts on the body. Hence, the magnitude of the net downward force on 1 the body = the magnitude of the weight of the body – the magnitude of the buoyant force on the body. Hence, when a spring balance is used to weigh a body, the weight of the body in air is less than that in vacuum.

Question 60.
What is density of a substance? I Obtain its SI unit.
Answer:
The density of a substance is the ratio of its mass to volume.
The SI unit of density = \(\frac{\text { the SI unit of mass }}{\text { the SI unit of volume }}\) = kg/m³
[Note: Density is useful in determining the purity of a substance. The CGS unit of density is g/cm³.
1 kg/m³ = 10³g/(100 cm)³ = 10^-3g/cm³
∴ 1g/cm³ = 1000 kg/m³]

Question 61.
What is relative density of a substance?
Answer:
The relative density of a substance is the ratio of its density to the density of water.
[Note: Relative density is also called specific gravity. It is a ratio of two equal (same) physical quantities. Hence, it has no unit.]

Question 62.
A piece of wood floats both in water and kerosine. In which liquid does it sink more during floating? Why?
Answer:
The piece of wood sinks more in kerosine than in water during floating. The density of kerosine is less than that of water. The buoyant force on a body is proportional to the density of the liquid in which the body is immersed. When a body floats, the magnitude of the buoyant force acting on the body is equal to that of the weight of the body.

Hence, the volume of the liquid displaced by a floating body is inversely proportional to the density of the liquid. As a result, when a piece of wood floats in kerosine, it displaces greater volume of kerosine compared to the volume of water displaced when the piece of wood floats in water. Hence, it sinks more in kerosine than in water.
[Note: When a body floats in a liquid fb = fg
∴ Vρ1g = Vbρbg
∴ The volume of the liquid displaced by the body is V = Vb \(\frac{\rho_{\mathrm{W}}}{\rho_{1}}\), where Vb is the volume of the body, ρb is the density of the material of the body and ρ1 is the density of the liquid. Thus, V ∝ 1 /ρ1]

Question 63.
State whether the body will float or sink in a liquid if the density of the body is 1. greater than that of the liquid 2. less than that of the liquid 3. equal to that of the liquid.
Answer:

1. The body will sink in the liquid if the density of the body is greater than that of the liquid.
2. The body will float in the liquid if the density of the body is less than that of the liquid.
3. The body will float inside the liquid if the density of the body is equal to that of the liquid.

Question 64.
If the relative density of a body is greater than 1, will it float in water?
Answer:
If the relative density of a body is greater than 1, it will not float in water.
[Note: The relative density of a pin is much greater than 1. But when kept gently on the surface of water, it floats. This is due to the surface tension of water.]

Question 65.
A glass of water has an ice cube floating in water. The water level must touches the rim of the glass. Will the water overflow when the ice melts? Give the reason.
Answer:
The water will not overflow when the ice melts. The water level will remain the same. Ice floats on water because its density is less than that of water. When ice melts, the volume of the water formed is less than the volume of the ice which has melted.

When ice in water melts, this difference equals the volume of the water formed when the part of ice above the surface of water melts. Therefore, the water level remains the same. Hence, there is no overflow of water when the ice melts.

Question 66.
A plastic ball is released underwater. State whether it will sink or come up to the surface of water. Give the reason.
Answer:
A plastic ball released under water will come up to the surface of water. The density of water is greater than that of plastic. Hence, when a plastic ball is under water, the magnitude of the buoyant force exerted by water on the ball is greater than the magnitude of the weight of the ball.

Therefore, the ball will start moving upward. As it comes up with part of the ball above the water surface, the volume of the water displaced by the ball becomes less and hence at a certain stage, the buoyant force and the weight balance each other. Then the ball continues to remain in that state, as the net force on the ball becomes zero.
[Note: Initially, the ball moves slightly up and down near the water surface. The force due to friction with water, opposing the motion of the ball, finally makes the ball steady.]

Write short notes:

Question 1.
Buoyant force.
Answer:
1. When a body is immersed partially or completely in a liquid, the liquid exerts forces on all sides of the body. This force is perpendicular to the surface of the body and equals the product of pressure and area at that point.

2. The resultant of all these forces acts upward. It is called the upthrust or buoyant force.

3. The buoyant force is proportional to (i) the volume of the liquid displaced by the body (ii) the density of the liquid (iii) the acceleration due to gravity. Its magnitude equals the magnitude of the weight of the liquid displaced by the body.

Question 2.
Applications of Archimedes’ principle.
Answer:
1. The working of a lactometer, a device used to determine the purity of a sample of milk, and a hydrometer, a device used to determine the density of a liquid, is based on Archimedes’ principle. The extent to which a lactometer floats (or sinks) depends on the density (and hence purity) of the milk. The same thing is true for a hydrometer. The greater the density of a liquid, the less is the extent to which a body sinks in it.

2. Archimedes’ principle is used in design of ships and submarines. A submarine is provided with large tanks at the front and the back. Its weight can be increased by filling the tanks with sea water or air from compressed air reservoirs. The weight can be decreased by pumping out water from the tanks by forcing compressed air in them. By controlling the weight, it can be made to sink or rise to the surface as desired.

3. The density of a body that floats or sinks in water or kerosine can be determined by. Archimedes’ principle.
4. The density of kerosine can be determined by Archimedes’ principle, using a body of material that is not affected by water and kerosine.

Give scientific reasons:

Question 1.
The tiles are placed over a slushy patch of ground to help cross It.
Answer:

1. Tiles have greater area than the area of our feet.
2. The weight of the person crossing the slushy patch is exerted over a large area of the tiles.
3. Therefore, there is a decrease in the pressure and hence the tiles do not sink much in the slushy patch of ground. This helps to cross the slushy patch of ground.

[Note: If there were no tiles, the feet will come in direct contact with the slushy ground. The area of the feet being less, the weight of the person will act over a smaller area. Therefore. there will be more pressure and hence the feet will sink into the slushy ground.]

Question 2.
Drawing pins have flattened heads.
Answer:

1. The head of a drawing pin is flattened and the other end is pointed.
2. When enough force is applied to the head of the pin, the pressure due to the force on the pointed end increases tremendously and the pin can be easily inserted in the drawing board.
3. When we press the flattened end, the force applied spreads over a larger area. This reduces the pressure of the reaction force acting on the thumb. Hence, the thumb is not injured.
4. If the head of the pin is sharp, then the pressure due to the force would be more and hence the pressure of the reaction force would also be more and the sharp end would prick the thumb causing injury.

Question 3.
An iron nail sinks in water but a ship made from iron floats on water.
Answer:
1. An iron nail sinks in water because its density is more than that of water.
2. A ship made from iron, due to the particular shape given to it, displaces a large amount of water so that the buoyant force acting on the ship due to water balances the weight of the ship. Hence, the ship floats on water.

Question 4.
A piece of iron sinks in water but floats on mercury.
Answer:
The density of iron is more than that of water but less than that of mercury. Hence, a piece of iron sinks in water but floats on mercury.

Question 5.
A sheet of metal that sinks in water can float if shaped like a pan.
Answer:

1. A sheet of metal sinks in water because its density is more than that of water.
2. If the sheet is shaped like a pan, it can displace a large amount of water such that the buoyant force on the pan due to water balances the weight of the pan. Hence, it can float on water.

Solve the following examples:

Problem 1.
(i) Calculate the pressure exerted by the wooden block when it is kept in the vertical position.
Given: The length of the wooden block is 80 cm, the breadth is 50 cm, the thickness is 20 cm and the weight is 500 N
(ii) Also calculate the pressure when the wooden block is kept in the horizontal position with its surface 80 cm × 50 cm touching the floor.

Solution:
Data: F = W = 500 N, l = 80 cm = 0.8 m, b = 50 cm = 0.5 m. h = 20 cm = 0.2 m
(i) A = bh = 0.5 m × 0.2 m = 0.1 m²

The pressure exerted in the vertical position of the block = 5000 N/m² or 5000 Pa.

(ii) A = lb = 0.8 m × 0.5 m = 0.4 m²

The pressure exerted in the horizontal position of the block = 1250 N/m² or 1250 Pa.

Problem 2.
Measure the length, breadth, height and mass of a rectangular tiffin box. Find the weight of the box and calculate the pressure in two different positions as in Ex. (1) above.
Solution:
Let l = 0.25 m, 6 = 0.1 m, h = 0.05 m, F = W= 0.5 N
(i) A = bh = 0.1 m × 0.05 m = 0.005 m²

(ii) A = lb = 0.25 m × 0.1 m = 0.025 m²

Problem 3.
A force of 1000 N is applied over an area 50 cm × 20 cm. Find the corresponding pressure.
Solution:
Data: F = 1000 N,
A = 50 cm × 20 cm = 0.5 m × 0.2 m = 0.1 m², pressure = ?

The pressure = 10 N/m².

Problem 4.
A metal block has thmensions 10 cm × 5 cm × 2 cm and the density of the metal is 8 × 10³ kg/m³. It is kept on a table with the face 10 cm × 5 cm in contact with the table. Find the force and pressure exerted by the block on the table. (g = 9.8 m/s²)
Solution :
Data : 1 = 10 cm, b = 5 cm,
h = 2 cm, p= 8 × 10 kg/m3, g = 9.8 m/s²,
A = lb = 10cm × 5cm = 50cm² = 50 × 104m²
= 5 × 10^-5m², force =?, pressure = ?
Volume of the block = lbh =
10 cm × 5 cm × 2 cm= 100 cm³
= 100 × 10^-6 m³ = 1 × 10^-4m³
Mass of the block = volume × density
(∵ density = mass/volume)
∴Mass of the block,
m = 1 × 10^-4 m³× 8 × 10³ kg/m³ = 0.8 kg
Weight of the block = mg = 0.8 kg × 9.8 m/s² = 7.84 N
∴ The force exerted by the block on the table = 7.84 N.
force 7.84 N

= 1.568 × 10³ N/m² or 1.568 × 10³ Pa
The pressure exerted by the block on the table = 1.568 × 10 N/m2 or 1.568 × 10³ Pa.

Problem 5.
A body of volume loo cm³ is immersed completely in water. Find the weight of the water displaced by the body. 1g = 9.8 m/s². p (water) = kg/m³]
Solution :
Data: V = 100 cm³ = 100 × 10^-6 m³
= 1 × 10 m³, p(water) = 10 kg/m³
g = 9.8 m/s², weight of the displaced water ?
Density = \(\frac{\text { mass }}{\text { volume }}\)
∴ Mass = volume × density
Volume of the water displaced by the body = l × 10^-4 m³
∴Mass of the water displaced,
m = l × 10^-4 m³ × 10 kg/m³ = 0.1 kg
∴Weight of the water displaced
= mg = 0.1 kg × 9.8 m/s² = 0.98 N.
The weight of the water displaced by the body = 0.98 N.

Problem 6.
A body of mass 200 g and volume 50 cm³ is put in a bucket containing water. Will it float or sink ?
[ρ(water) = 1 g/cm³]
Solution:
Data: m = 200 g, V= 50 cm³,
ρ (water) = 1 g/cm³
Density(ρ) = \(\frac{\text { mass }}{\text { volume }}\)
∴ ρ (body) = \(\frac{200}{50 \mathrm{~cm}^{3}}\)
It is greater than the density of water.
Hence, the body will sink in water.

Problem 7.
A body of mass 200 g and volume 400 cm³ is put in a bucket containing water. Will it float or sink?
[ρ (water)=1 g/cm³]
Solution:
Proceed as above.
ρ (body) = \(\frac{200 \mathrm{~g}}{400 \mathrm{~cm}^{3}}\) = 0.5 g/cm³
It is less than the density of water.
∴ The body will float in water.

Problem 8.
The mass of a tile is 500 g. If the density of the tile is 2.5 g/cm³, what will be the weight of the tile when it is completely immersed in water?
(g = 9.8 m/s², ρ(water) = 1000 kg/m³)
Solut10n:
Data: m = 500, g = 0.5 kg, ρ
(tile) = 2.5 g/cm³ = 2500 kg/m³, g = 9.8 m/s²,
ρ (water) = 1000 kg/m³, weight of the tile when completely immersed in water (also called the apparent weight) = ?
ρ = \(\frac{m}{V}\)

∴ Volume of water displaced by the tile
= 2 × 10^-4 m³
∴ Mass of water displaced by the tile
m’ = ρ (water) V = 1000 kg/m³ × 2 × 10^-4 m³
= 0.2kg
∴ Magnitude of the weight of this water
= mg = 0.2 kg × 9.8 m/s² = 1.96 N
∴ Buoyant force exerted on the tile = 1.96 N
Magnitude of the weight of the tile =
mg = 0.5 kg × 9.8 m/s² = 4.9 N
∴ Weight of the tile when completely immersed in water (apparent weight) = weight of the tile in air-buoyant force on the tile
= 4.9 N – 1.96 N = 2.94 N(downward)

Examples For Practice:

[g = 9.8 m/s², ρ (water) = 10³ kg/m³ = 1 g/cm³]

Question 1.
Calculate the relative density of a metal having density 7.5 g/cm³.
Answer:
7.5

Question 2.
Find the density of steel if its relative density is 8 and the density of water is 10 kg/m³.
Answer:
8 × 10³ g/cm³

Question 3.
A body has mass 200 g and volume 100 cm³. Find its density and relative density.
Answer:
2 g/cm³, 2

Question 4.
If the relative density of a material is 2.5, find its density.
Answer:
2.5 × kg/m³ or 2.5 g/cm³

Question 5.
A force of 100 N is applied on an area 40 cm × 25cm. Find the corresponding pressure.
Answer:
10³ N/m²

Question 6.
If the pressure exerted on an area 10 cm × 10 cm is 1000 dynes/cm², find the applied force.
Answer:
10⁵ dynes

Question 7.
A metal block of mass 10 kg is kept on a table. If the contact surface area Is 100 cm², find the pressure on the table.
Answer:
9.8 × 10³ N/m² or 9.8 × 10³ Pa

Question 8.
A body of volu.me 50 cm³ is immersed completely in water. Find the weight of the water displaced by the body.
Answer:
0.49 N

Question 9.
A block of mass 100 g and volume 20 cm³ is put in a bucket filled with water. Will it float or sink?
Answer:
The body will sink in water.

Question 10.
Will a block of mass 100g and volume 400 cm³ float or sink in water?
Answer:
The block will float in water.

Question 11.
The volume of a cube is 125 cm³ and its mass is 250 g. It is put in a tub containing water. Will it float or sink?
Answer:
It will sink in water.

Balbharti Maharashtra State Board Class 8 Civics Solutions Chapter 1 Introduction to the Parliamentary System Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Civics Solutions Chapter 1 Introduction to the Parliamentary System

Class 8 Civics Chapter 1 Introduction to the Parliamentary System Textbook Questions and Answers

1. Choose the correct option and rewrite the statements:

Question 1.
Parliamentary System of government developed in ……………. .
(a) England
(b) France
(c) United States of America
(d) Nepal
Answer:
(a) England

Question 2.
In the Presidential System, ……….. is the executive head.
(a) Prime Minister
(b) Lok Sabha Speaker
(c) President
(d) Governor
Answer:
(c) President

2. Complete the information in the following table.

Question 1.

Answer:

3. Explain the following statements with reasons:

Question 1.
India adopted the Parliamentary System of government.
Answer:

1. The Parliamentary System of government developed primarily in England.
2. The British ruled over India for about 150 years. During this period, they ruled in accordance with this system.
3. So, Indians were familiar with this system of government.
4. The Constituent Assembly also adopted this system after a thorough discussion.
5. Hence, the framers of the Constitution made a few changes to suit the Indian situation, and adopted the Parliamentary System.

Question 2.
Discussions and deliberations are important in a Parliamentary System of government.
Answer:

1. In a Parliamentary System of government, decisions are taken after discussions and deliberations.
2. Members of the opposition party also participate in the discussions.
3. They may support the government or point out shortcomings in the government policies.
4. Laws are framed after detailed discussions on questions of public welfare. This does not happen in autocratic rule.
5. Hence, to protect the welfare and freedom of common people, discussions and deliberations are important.

4. Answer the following in 25 to 30 words:

Question 1.
What is a Responsible Government?
Answer:

1. The government system in which the Prime Minister and the Council of Ministers is responsible to the Legislature for all their actions and policies, is called a Responsible Government.
2. In this system, the Council of Ministers has to take the Legislature into confidence during governance.
3. Every decision taken by any ministry/ department is considered as the decision of the government.
4. The decisions or policies of every ministry is the collective responsibility of the Council of Ministers.
5. Thus, the principle of collective responsibility adopted by the Council of Ministers makes it a responsible government.

Question 2.
Enumerate the characteristics of the Presidential System of government.
Answer:
The following are the characteristics of the Presidential System of government:

1. The President is directly elected by the people.
2. The President has lot of powers including power to implement laws.
3. The President is not dependent on the support of the Legislature.
4. The Legislature and the Executive are not dependent on each other, but still they have mutual control over each other.

5. Why is the role of opposition parties important? Write your opinion.

Question 1.
Why is the role of opposition parties important? Write your opinion.
Answer:
The role of opposition parties is important in Parliamentary as well as Presidential System of government.

1. The opposition parties participate in the discussions and point out the shortcomings in the policies of the government.
2. The opposition parties control the Executive through their arguments based on deep study of the topics discussed in the Parliament.
3. The Executive cannot behave in an irresponsible manner due to the pressure of the opposition parties.
4. The alertness of the opposition parties help in avoiding wrong practices like corruption, ignoring public welfare, passing faulty laws, etc.

Have you thought of this?

1. What is a parliamentary system of government?
2. In India we have Prime Minister but why is there no Prime Minister in the United States of America?
3. What is the difference between a Parliamentary and a Presidential system of government?

Project:

Watch the live telecast proceedings of the Lok Sabha and Rajya Sabha on the national channel Doordarshan and write your observations.

Class 8 Civics Chapter 1 Introduction to the Parliamentary Additional Important Questions and Answers

Choose the correct option and rewrite the statements:

Question 1.
The interrelationship between the Legislature, Executive and Judiciary is decided by the …….
(a) Government
(b) Presidential System
(c) Constitution
(d) Parliament
Answer:
(c) Constitution

Question 2.
The English Constitution is an …….. Constitution where governance is based on conventions.
(a) changeable
(b) unchangeable
(c) unwritten
(d) written.
Answer:
(c) unwritten

Question 3.
Sometimes, when no party gets a clear majority, ……… government is formed.
(a) Presidential
(b) coalition
(c) Military
(d) communist
Answer:
(b) coalition

State whether the following statements are True or False. Correct the False statement and rewrite:

Question 1.
Parliamentary System of government is considered as a contribution of United States of America.
Answer:
False.
Correct: Parliamentary System of government is a contribution of England.

Question 2.
In the Parliamentary System, the Legislature of the Central Government is known as the ‘Parliament’.
Answer:
True.

Question 3.
Members of the opposition party also take part in the discussion of the questions related to public welfare.
Answer:
True.

Question 4.
In the Parliamentary System, the President is directly elected by the people.
Answer:
False.
Correct: In the Presidential System, the President is directly elected by the people.

Find and write:

Complete the concept map:

Question 1.

Answer:

Question 2.

Answer:

Question 3.

Answer:

Write short notes:

Question 1.
Characteristics of Parliamentary System of India:
Answer:
The following are the characteristics of Parliamentary System adopted by India:

1. The Parliament of India is composed of the President, Lok Sabha and Rajya Sabha.
2. Fixed number of members of the Parliament are directly elected by the people.
3. All political parties contest elections, which are held at regular intervals.
4. The party having majority in Lok Sabha or a coalition government comes into power.
5. The leader of the majority party becomes the Prime Minister and he selects candidates to form the Council of Ministers.
6. The Executive has to perform the responsibility of its individual minister¬ship as well as the responsibility of the Legislature, for all their actions and policies.

Question 2.
Responsibilities of the Executive in India:
Answer:
The Executive in India has to fulfill following responsibilities:

1. Implementing the laws passed by the Parliament.
2. Framing policies for governing the nation.
3. Functioning as the members of the Legislature.
4. Striving to develop the nation through decisions related to the welfare of the people.

Explain the following statements with reasons:

Question 1.
No-confidence motion is an effective tool of keeping a check over the Executive.
Answer:

1. In the Parliamentary System, the Executive is dependent upon the confidence of the Legislature in them.
2. If the Legislature feels that the Executive does not work in accordance to its wishes, it can pass a no-confidence motion against the Executive.
3. If the Legislature passes the no-confidence motion with a majority, then the Executive has to resign.
4. The Constitution has provided this tool to prevent the Executive from misusing its powers.
   Hence, no-confidence motion is an effective tool of keeping a check over the Executive.

Question 2.
The Parliament is of great importance in the Parliamentary System of government.
Answer:

1. In the Parliamentary System of government the members of the Legislature are directly elected by the people.
2. Since the elected members represent the people of the nation in the Parliament, they express and carry the hopes and wishes of the people.
3. The Parliament decides the policies for the welfare of the people.
4. If the Parliament feels that the Executive does not work in accordance to its wishes, it can remove the Executive from power by passing a no-confidence motion against it.

Since, the Parliament reflects the wishes and opinions of the people of the nation, it is of great importance.

Have you thought of this?

Question 1.
What is a Parliamentary System of government?
Answer:

1. The Parliamentary System of government is the one where representatives are directly elected by the people.
2. They are the members of the Legislature, which is also known as the Parliament.
3. In this system, elections are held after fixed period.
4. The party which gets the majority forms the government.
5. In this system, the Executive is dependent on the confidence of the Legislature.

Question 2.
In India we have Prime Minister but why is there no Prime Minister in the United States of America?
Answer:

1. In the Parliamentary System of government, the Prime Minister is the head of the Executive, i.e. the Council of Ministers.
2. In the Presidential System of government, the President is the head of the Executive. ‘
3. Since India has adopted the Parliamentary system, we have the post of the Prime Minister.
4. Since United States of America has adopted Presidential System, they have the post of the President.
5. The post of the Prime Minister does not exist in Presidential System of government.

Question 3.
What is the difference between a Parliamentary and a Presidential System of government?
Answer:
Difference between the Parliamentary and Presidential System of government is as follows:

Question 4.
Why is the role of opposition parties important? Write your opinion.
Answer:
The role of opposition parties is important in Parliamentary as well as Presidential System of government.

1. The opposition parties participate in the discussions and point out the shortcomings in the policies of the government.
2. The opposition parties control the Executive through their arguments based on deep study of the topics discussed in the Parliament.
3. The Executive cannot behave in an irresponsible manner due to the pressure of the opposition parties.
4. The alertness of the opposition parties help in avoiding wrong practices like corruption, ignoring public welfare, passing faulty laws, etc.

Balbharti Maharashtra State Board Class 8 Civics Solutions Chapter 2 The Indian Parliament Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Civics Solutions Chapter 2 The Indian Parliament

Class 8 Civics Chapter 2 The Indian Parliament System Textbook Questions and Answers

1. Complete the following sentences by choosing the correct option.

Question 1.
Candidates to the Lok Sabha are elected through ……….. .
(a) Territorial constituencies
(b) Religious constituencies
(c) Local bodies
(d) Proportional Representation System
Answer:
(a) Territorial constituencies

Question 2.
The ………….. of India is the ex-officio chairman of the Rajya Sabha.
(a) President
(b) Vice-President
(c) Prime Minister
(d) Chief Justice
Answer:
(b) Vice-President

2. Find and write. 

Question 1.
Members of Lok Sabha and Rajya Sabha are known as ……………….. .
Answer:
Members of Parliament (MPs)

Question 2.
The responsibility of making laws is with the ……………… .
Answer:
Parliament

3. Explain the following statements with reasons:

Question 1.
Rajya Sabha is a permanent House.
Answer:

1. The tenure of the members of Rajya Sabha does not get over at the same time.
2. 1/3rd of the total membership of Rajya Sabha retire after every two years and equal number of new members get elected.
3. Because the limited members of Rajys Sabha retire step by step, it can function continuously.
   Since Rajya Sabha is never dissolved completely it is called a permanent House.

Question 2.
Lok Sabha is known as the first House.
Answer:

1. Lok Sabha is the lower and the first House of the Parliament of India.
2. Lok Sabha is the House of Representatives directly elected by the people. Hence, Lok Sabha is known as the first House.

4. Answer the following in 25 to 30 words:

Question 1.
How are members of the Lok Sabha elected?
Answer:

1. As per the Constitution, there can be a maximum of 552 members in Lok Sabha.
2. General elections to Lok Sabha are held after every five years and members are directly elected by the people.
3. To ensure equal representation to all sections of the community, some seats are reserved for members belonging to Scheduled Castes and Scheduled Tribes.
4. In case there are no representation from the Anglo-Indian community, the President can appoint two members from this community to the Lok Sabha.
5. Thus, Lok Sabha is the representative body of the citizens of India.

Question 2.
Explain the functions of the Speaker of Lok Sabha.
Answer:
The functions of the Speaker of Lok Sabha are :

1. To conduct the business of the House in an unbiased manner.
2. To take care of the rights and privileges of the members of Lok Sabha.
3. To interpret the rules of daily functioning of the House and work accordingly.
4. To maintain the decorum and dignity of the House.

5. Explain the step involved in the lawmaking process.

Question 1.
Parliament :
Answer:

1. The Legislature at the national level is called the Parliament.
2. It consists of the President and two houses, i.e., the Lok Sabha and the Rajya Sabha.
3. Though the President is an inseparable part of the Parliament, he/she cannot participate in the discussions in either of the Houses of the Parliament.
4. The Constitution of India has created the Parliament.

Question 2.
Amendment to the Constitution :
Answer:

1. According to the changing times, certain necessary changes have to be made in some laws. The process of making such changes is called Amendment.
2. Only the Parliament has the right to make such amendments to the Constitution.
3. The Constitution amendment bill is considered to be an important bill.
4. The Parliament discusses why the amendment is required and decides whether to accept it or not.

Question 3.
Members of Parliament :
Answer:

1. The members of Lok Sabha and Rajya Sabha are known as Members of Parliament (MPs).
2. The members of Lok Sabha are directly elected by the people.
3. The members of Rajya Sabha are elected from the constituent States and Union Territories.
4. MPs try to resolve the queries and complaints of their constituencies by raising questions in the Parliament.
5. MPs also participate in the process of formulation of laws.
6. The Government allocates funds to MPs to carry out development activities in their constituencies.

Question 4.
Bill of Law:
Answer:

1. At the initial stage of lawmaking process, a rough draft of the law is prepared.
2. This rough draft or outline is known as ‘draft proposal of the law’ or ‘bill of law’.
3. The Bill clearly mentions the objectives and the details of the proposed law.
4. Every bill has to undergo three readings in both the Houses, and then it is put to vote.

Can you find out?

For the purpose of elections, the State is divided into territorial constituencies. The constituent States in India get seats on the basis of their population. For e.g.

• Maharashtra – 48 seats
• Gujarat – 26 seats
• Madhya Pradesh – 29 seats
• Goa – 02 seats
• Uttar Pradesh – 80 seats

Understand It:
(The gist of the conversation held between Mazy, Radhika, Ran veer and others.)

1. Any Indian citizen who has completed 18 years of age is only eligible to vote.
2. An Indian citizens who has completed 25 years of age can contest for Lok Sabha election.
3. A citizen of India can contest for election from any constituency of any State.
4. Citizens of other countries cannot contest for elections of Lok Sabha and Rajya Sabha.
5. Just as there are set criteria for qualifying for election, there are set criteria for disqualification as well.

Rights regarding passing of Bills:

1. Though Lok Sabha and Rajya Sabha have same set of rights, Lok Sabha has certain rights which are not available for Rajya Sabha.
2. Bills related to finance (Money Bills) and such other bills are first introduced and passed in Lok Sabha.
3. Rajya Sabha has limited powers with respect to money bills.
4. Rajya Sabha can pass a resolution on the subject in the State List.

Can you tell?

Certain laws which become out-of-date (obsolete) are abolished. Can you give examples of such obsolete laws? For example, Privy purses.

Know this too:

1. Every year, on 1 February the Union Finance Minister presents the national budget to the Lok Sabha. Previously, it was presented on 28 February.
2. The State Legislatures also follow the same procedure of law making as in the Parliament.
3. The bill passed can become a law only after it is signed by the President at the Union level and by the Governor at the State level.

Project:

The President nominates 12 members to the Rajya Sabha. Collect information on what are the criteria for their selection.

Class 8 Civics Chapter 2 The Indian Parliament Additional Important Questions and Answers

Complete the following sentences by choosing the correct option:

Question 1.
…………….. is the upper House of the Parliament.
(a) Legislative Assembly
(b) Lok Sabha
(c) Rajya Sabha
(d) Legislative Council
Answer:
(c) Rajya Sabha

Question 2.
The …………… of India has created the Parliament of India.
(a) Legislature
(b) Executive
(c) Constitution
(d) British Law
Answer:
(c) Constitution

Question 3.
1/3rd members of total membership of Rajya Sabha, who have completed their tenure of six years, retire after every ……………….. years.
(a) two
(b) four
(c) five
(d) six
Answer:
(a) two

Question 4.
If ……………….. feels that the Parliament should make a law of the subject in the state list, it can pass a resolution to that effect.
(a) Lok Sabha
(b) Rajya Sabha
(c) Executive
(d) President
Answer:
(b) Rajya Sabha

Question 5.
Every year in the month of February, the ………….. presents the national budget to the Lok Sabha.
(a) Prime Minister
(b) President
(c) Finance Minister
(d) Speaker
Answer:
(c) Finance Minister

Question 6.
The President appoints ……………….. distinguished personalities to the Rajya Sabha.
(a) two
(b) eight
(c) fifteen
(d) twelve
Answer:
(d) twelve

Find and write:

Question 1.
……………. represent the Lok Sabha.
Answer:
The Speaker

Question 2.
The bill passed by the State legislature becomes a law after it is signed by the ………….. .
Answer:
Governor

Question 3.
The House that gives representation to 29 States and 7 Union Territories is ………………. .
Answer:
Rajya Sabha

Complete the following Concept maps:

Question 1.

Answer:

Question 2.

Answer:

Question 3.

Answer:

Write short notes on:

Question 1.
The Chairman of Rajya Sabha :
Answer:

1. The Vice-President of India is the ex-officio Chairman of Rajya Sabha.
2. He exercises a control over the functioning of Rajya Sabha.
3. Maintaining discipline in the House is the function of the Chairman of Rajya Sabha.
4. He also has the responsibility of facilitating discussions in the House by giving members a chance to speak, etc.

Question 2.
Speaker of Lok Sabha :
Answer:

1. The speaker is elected in the very first meeting after the election of Lok Sabha.
2. The members of Lok Sabha elect one member among them as the Speaker.
3. Lok Sabha functions under the guidance and control of the Speaker.
4. It is the responsibility of the speaker to conduct the business of the House in an unbiased manner.
5. The Speaker has to maintain decorum and dignity of the House.
6. Moreover, he has to interpret the rules and work accordingly.

Question 3.
Control over Council of Ministers :
Answer:

1. Council of Ministers are drawn from the Parliament and hence Parliament exercises control over them.
2. The members of Parliament exercise this control through multiple ways.
3. It is the responsibility of the Parliament to see that the Council of Ministers does not disregard the Parliament.
4. In case the Lok Sabha passes a no-confidence motion against the Council of Ministers, it has to resign.

Answer the following in 25 to 30 words :

Question 1.
Write about Lok Sabha elections.
Answer:

1. Since Lok Sabha is a House of people’s representatives, elections are held after every five years.
2. Elections to Lok Sabha which are held every five years are known as General elections.
3. When Lok Sabha is dissolved before the completion of five years and elections are held, such elections are called mid- term elections.
4. When a member resigns or dies suddenly, election held for such a seat is called by-election.

Question 2.
Explain the composition of Rajya Sabha.
Answer:
The composition of Rajya Sabha is as follows :

1. The total membership of Rajya Sabha is 250 members.
2. Amongst them, 238 members are elected from the constituent states and Union Territories.
3. Remaining twelve members, who are distinguished personalities from the fields of literature, arts, science, sports and social work, are appointed by the President.
4. The members of Rajya Sabha are elected through the system of proportional representation.

Question 3.
Explain the functions of the Parliament.
Answer:
In order to achieve welfare of the people and the objectives of the 8 Constitution, the Parliament has to perform 8 following functions :

1. To formulate new laws and to repeal the outdated laws.
2. To make necessary changes in the existing laws.
3. To amend the Constitution wherever necessary.
4. To keep control over Council of Ministers.

Question 4.
Mention the ways of amending the Constitution.
Answer:
The Constitution can be amended in following ways :

1. Few provisions in the Indian Constitution can be amended by simple majority.
2. Some provisions require special (2/3rd) majority of the Parliament.
3. Few other provisions can be amended by special majority plus consent from more than half of the constituent states.

Explain the following statements with reasons:

Question 1.
Though Lok Sabha is the Lower House, it is more powerful than Rajya Sabha.
Answer:

1. Since members of Lok Sabha are directly elected by the people, it represents the people of the nation in the true sense.
2. Money bills related to financial matters are presented in Lok Sabha. Rajya Sabha has very limited powers with respect to Money Bills.
3. Since the total membership of Lok Sabha is more than Rajya Sabha, it always gets an upper hand when decisions are taken in the joint meeting of both the Houses.
4. Only Lok Sabha can pass a no-confidence motion against the Council of Ministers.

Hence, though Lok Sabha is the lower House, it is more powerful than Rajya Sabha.

Answer the following questions in details:

Question 1.
Explain the steps involved in the law-making process.
Answer:
The Bill undergoes following process in order to be converted into a Law (Act).
1. First reading :

• The minister of the concerned department/ministry or member of the Parliament presents the bill in the House.
• The objectives and the structure of the Bill are mentioned.

2. Second reading :

• The positive and negative points of the bill are discussed.
• The defects and faults in the bill are stressed.
• After removing the defects and the faults, the bill is put to vote.

3. Committee Stage :

• Sometimes, if required, the Bill is sent to the committee of the House.
• The Bill is discussed in the Committee in details.
• The Committee report consisting of instructions and recommendations is sent to the House.
• The Bill is discussed clause by clause and then voting is taken.

4. Third reading :

• The Bill is once again discussed in the House.
• Voting is taken for approving the Bill.

5. Approval of the other House :

• The Bill has to undergo the same procedure even in the other House.
• The Bill is approved by majority.

6. Assent by the President :

• After getting an approval from both the Houses, the Bill is further sent for assent by the President.
• After the final assent and signature of the President, the Bill is converted into Law.

Question 2.
Distinguish between Lok Sabha and Rajya Sabha on the basis of following points:
1. Number of members
2. Age limit
3. Election
4. Tenure
Answer:

Question 3.
Why, according to you, the Constitution must have granted the President, the right to appoint twelve members to the Rajya Sabha?
Answer:
1. The President appoints twelve members to the Rajya Sabha. These members are usually experienced and distinguished personalities from the fields of literature, arts, science, sports and social service.

2. Such personalities are very active and totally devoted to their respective fields. Hence, they have no time for contesting the elections.

3. They keep themselves away from election procedures like campaigning, conducting meetings, etc. So their election to the Parliament is not possible.

4. But, to derive benefit from their profound knowledge and experience for making of laws, their presence in the Parliament is essential.
Therefore, I feel that the Constitution has granted the President, the right to appoint twelve members to the Rajya Sabha.

Balbharti Maharashtra State Board Class 8 Geography Solutions Chapter 10 Field Visit Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Geography Solutions Chapter 10 Field Visit

Class 8 Geography Chapter 10 Field Visit Textbook Questions and Answers

Question a.
Prepare a questionnaire for a visit to a NGO working for cleanliness of marine beaches.
Answer:
A questionnaire for a visit to a NGO working for cleanliness of marine beaches is as follows :

1. What is the year of establishment of this NGO?
2. What are the aims and objectives of this NGO?
3. Which activities/programmes are carried out for the cleanliness of marine beaches?
4. How are the people from surrounding areas involved in those various activities and programmes?
5. What are the future plans of this NGO?

Field trip:

• Nature: Field trip is an important study method in geography.
• Importance: Field trip helps in understanding various geographical concepts, elements and processes through direct experiences. It helps in understanding the correlation between humans and environment.
• Planning: Planning of field trip includes deciding the aim, place, duration, etc. about the field trip.
• Preparations : Preparations of field trip includes deciding the place of field visit, maintaining essential materials like notebook, pen, pencil, camera, etc., deciding the schedule for field visit, preparing questionnaire, etc.
• Precautions : One should ensure that there is no harm to the environment in any way during field trip /visit.

Report writing:

• Nature : A field report should be written on the basis of information obtained after field visit is complete.
• Basis : The field report can be written on the basis of information gathered from field visit, photographs, maps, informative charts, questionnaire, etc.
• Points : The field report can be written with the help of the following points :
  (a) Introduction
  (b) Presentation of information obtained
  (c) Conclusion, etc.

Field trips help in enhancing the understanding and sensitivity about the historical, economic, social, and cultural facts about the selected field. Report on field visit should be presented in the classroom.

Balbharti Maharashtra State Board Class 8 Geography Solutions Chapter 3 Humidity and Clouds Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Geography Solutions Chapter 3 Humidity and Clouds

Class 8 Geography Chapter 3 Humidity and Clouds Textbook Questions and Answers

1. Match the column and complete the chain: 

Answer:

2. Choose the correct word from the brackets and complete the sentences:
(Options: Cumulonimbus, relative humidity, absolute humidity, condensation, vapor-holding capacity)

Question a.
The ………….. of the air is dependent on the temperature of the air.
Answer:
vapour-holding capacity

Question b.
The amount of vapour in 1 cu.m, of air shows the ………….
Answer:
absolute humidity

Question c.
As …………. is less in the desert areas, the air is dry there.
Answer:
relative humidity

Question d.
……………. type of clouds are indicators of the storm.
Answer:
Cumulonimbus

Question e.
In a free environment, the ………….. of the vapour present in the atmosphere takes place around the dust particles.
Answer:
condensation

3. Differentiate between: 

Question a.
Humidity and clouds:
Answer:

Question b.
Relative humidity and Absolute humidity
Answer:

Question c.
Cumulus clouds and Cumulonimbus clouds
Answer:

4. Answer the following questions:

Question a.
Why is the air in a region dry?
Answer:
Due to the low amount of the moisture in the air, the air in a region is I dry.

Question b.
How is humidity measured?
Answer:
1. The amount of water vapour in 1 cu.m, of air is called the absolute humidity.

2. Absolute humidity is measured with the help the following formula:
Absolute humidity
= \(\frac{\text { Mass of water vapour }}{\text { Volume of air }}\)

3. The amount of water vapour present in air expressed as a percentage of the amount needed for saturation at the same temperature is called relative humidity.

4. Relative humidity is measured with the help of the following formula: Relative humidity (%)

Question c.
What are the prerequisites for condensation?
Answer:
High relative humidity and dew point temperature of the air are the j prerequisites for condensation.

Question d.
What is a cloud? Write its types.
Answer:
A. Meaning:
A visible mass of fine particles of ice and water accumulated around the dust particles in the air at high altitude is called a cloud.

B. Types:
The following are the types of clouds:

1. High clouds: Clouds at an altitude of 7000 m to 14000 m are considered as high clouds. Cirrus, Cirro-Stratus and CirroCumulus are high clouds.
2. Medium clouds: Clouds at an altitude of 2000 m to 7000 m are considered as medium clouds. Alto-Stratus and Alto Cumulus are medium clouds.
3. Low clouds: Clouds at an altitude of less than 2000m are considered as low clouds. Strato-Cumulus, Stratus, Nimbostratus, Cumulus and Cumulonimbus are low clouds

Question e.
Which type of clouds give rain?
Answer:
Nimbostratus and cumulonimbus type of clouds give rain.

Question f.
On what does the percentage of relative humidity depend?
Answer:
The percentage of relative humidity depends on the absolute humidity and vapour-holding capacity of the air at a given temperature.

5. Give geographical reasons:

Question a.
Clouds float in the sky.
Answer:

1. The condensed water or fine particles of snow accumulate around dust particles at high altitudes leading to formation of clouds.
2. The condensed water or fine particles in the clouds are almost weightless. Therefore, clouds float in the sky.

Question b.
The proportion of relative humidity changes according to altitude.
Answer:
1. The temperature is found to be comparatively high in the areas at sea level. Due to high temperature, moisture-holding capacity of air near sea level is found to be high. Therefore, the humidity of the air at sea level is comparatively high.

2. The temperature is found to be comparatively low in the areas at high altitude. Due to low temperature, moisture-holding capacity of air at high altitudes is found to below. Therefore, the humidity of the air at high altitude is comparatively low. In this way, the proportion of relative humidity changes according to the altitude.

Question c.
Air becomes saturated.
Answer:

1. At certain temperature, the moisture-holding capacity of air gets fulfilled and it becomes equal to the proportion of the moisture present in it.
2. At this state, no more moisture can be absorbed by the air. Thus, air becomes saturated.

Question d.
Cumulus clouds change into cumulonimbus clouds.
Answer:

1. Cumulus clouds are found between 500 m to 6000 m altitude. They are mostly formed due to the vertical flow of the air.
2. Sometimes, the vertical expanse of the cumulus clouds increases and it leads to formation of huge mountain-like cumulonimbus clouds. Thus, cumulus clouds change into cumulonimbus clouds.

6. Solve the following:

Question a.

When the temperature of the air is 30° C, its vapour-holding capacity is 30.37 gms/cu.m., If absolute humidity is 18 gms/cu.m., then what will be the relative humidity?
Answer:
Relative humidity (%)

Question b.
What would be the absolute humidity of air if 1 cu.m, air contains 4.08 gms of vapour at 0° C temperature.
Answer:
Absolute humidity

7. Collect the weather related information from newspapers for the month of July. Relate the difference in the maximum and minimum temperatures with humidity.

Activity:

Question a.
Make a table showing the types of clouds. Use various photographs.
Answer:

Class 8 Geography Chapter 3 Humidity and Clouds Additional Important Questions and Answers

Examine the following statements and correct the incorrect ones:

Question a.
Cumulonimbus clouds are the indicators of the pleasant atmosphere.
Answer:
Incorrect.
Correct statement: Cumulonimbus clouds are the indicators of the thunderstorm.

Question b.
The relative humidity is found to be high in desert region.
Answer:
Incorrect.
Correct statement: The relative
humidity is found to be less in desert region.

Question c.
The high temperature of the air leads to rapid evaporation.
Answer:
Correct.

Question d.
When the humidity in the air is 0 gm/cu.m. at any temperature, the air is said to be humid.
Answer:
Incorrect.
Correct statement: When the humidity in the air is o gm/cu.m. at any temperature, the air Is said to be dry.

Question e.
Cirrostratus appears like a bed sheet with wrinkles.
Answer:
Correct.

Answer the following questions in one sentence each:

Question a.
What is evaporation?
Answer:
The process of converting water into steam or water vapour is called evaporation.

Question b.
What is meant by the moisture-holding capacity of air?
Answer:
The capacity of air to hold moisture at a given temperature, is called the moisture-holding capacity of air.

Question c.
What is meant by the saturation of the air?
Answer:
The condition of air at a certain temperature, in which the moisture-holding capacity of air becomes equal to the I proportion of moisture present in it, is called saturation of the air.

Answer the following questions in brief:

Question a.
Write in brief about the features of high clouds.
Answer:
Clouds at an altitude of 7000 m to 14000 m are considered as high clouds. High clouds are mainly made up of ice particles. Cirrus, Cirro-Stratus and Cirro-Cumulus are high clouds. The following are the features of high clouds :

1. Cirrus: Cirrus are wispy.
2. Cirro-Stratus: Cirro-Stratus look like bed sheet with wrinkles. A halo is generally seen around these clouds.
3. Cirro-Cumulus clouds: Cirro- Cumulus look like groups of small waves.

Question b.
Write in brief about the features of medium clouds.
Answer:
Clouds at an altitude of 2000 m to 7000 m are considered as medium clouds. Alto-Stratus and Alto-Cumulus are medium clouds. The following are the features of medium clouds :

1. Alto-Stratus : Alto-Stratus are comparatively thin. The sun is visible through these clouds as if seen through a milky glass.
2. Alto-Cumulus : Alto-Cumulus are in the form of layers. They have wave-like structure. They are white in colour and have a grey shade.

Question c.
Write in brief about the features of Strato-Cumulus, Stratus and Nimbostratus.
Answer:
The features of Strato-Cumulus, Stratus and Nimbostratus are as follows :

1. Strato-Cumulus: Strato-Cumulus have layers. These clouds are mostly seen in round clusters. They are white to earthy in colour.
2. Stratus: Stratus are found in layers. They have uniform base. They are ash coloured.
3. Nimbostratus: Nimbostratus have thick layers. They are greyish in colour. They cause continuous rainfall. They are also responsible for snowfall.

Question d.
Write in brief about the features of Cumulus and Cumulonimbus.
Answer:
The features of Cumulus and Cumulonimbus are as follows :
1. Cumulus : Cumulus are found between 500 m to 6000 m altitude. They are mostly formed due to the vertical flow of the air. They have huge size and dome-like shape. They are grey in colour. They indicate pleasant atmosphere. With an increase in the vertical expanse, these clouds turn into cumulonimbus clouds and bring rain.

2. Cumulonimbus : Cumulonimbus appear like huge mountain. They are dense and dark in colour. They have anvil-like shape at the top. They are the indicators of thunder, lightning and storm. They bring rain with storm. Sometimes they also bring hailstones. The raindrops of these clouds are found to be larger in size.

Give geographical reasons for the following:

Question a.
The absolute humidity of air in coastal region is higher than humidity of air in inland areas.
Answer:
1. The rate of evaporation is found to be high in the coastal region. As its effect, the amount of moisture in air in coastal region is found to be high. This results in high absolute humidity of air in coastal region.

2. On the other hand, the rate of evaporation is found to be low in the inland areas. As its effect, the amount of moisture in air in inland regions is found to be low. This results in low absolute humidity of air in inland areas. Thus, the absolute humidity of air in coastal region is higher than humidity of air in inland areas.

Question b.
The absolute humidity of air in equatorial region is higher than humidity of air in polar region.
Answer:
1. Equatorial region receives perpendicular sunrays throughout the year leading to high temperature. High temperature increases the rate of evaporation and this further leads to high absolute humidity of air in equatorial region.

2. Polar regions receive extremely slanted sunrays throughout the year leading to very low temperature. Very low temperature decreases the rate of evaporation and this further leads to very low absolute humidity of air in polar region. Thus, the absolute humidity of air in equatorial region is higher than humidity of air in polar region.

Question c.
Damp air is found in the coastal regions.
Answer:

1. The rate of evaporation is found to be high in the coastal region. As its effect, the amount of moisture in air in coastal region is found to be high.
2. The absolute humidity of the air near coastal region is found to be high. Therefore, damp air is found in the coastal regions.

Question d.
Dry air is found in the inland regions.
Answer:

1. The rate of evaporation is found to be low in inland region. As its effect, the amount of moisture in air in inland region is found to be low.
2. The absolute humidity of the air in inland region is found to be low. Therefore, dry air is found in inland regions.

Differentiate between the following :

Question a.
Densification and Sublimation :
Answer:

Study the following map/figure /graph and answer the following questions:

1. Study the figure 3.7 given on page 20 of the textbook and answer the following questions :

Question a.
What is the maximum diameter of the raindrop?
Answer:
The maximum diameter of the raindrop is 5 mm.

Question b.
Around what does the condensation of the water vapour in the air occur?
Answer:
The condensation of the water vapour in the air occurs around the minute particles of dust or salt in the air.

2. Study the Figure 3.9 given on page 22 of the textbook and answer the following questions :

Question a.
Which type of charge is found at the upper end of the cumulonimbus clouds?
Answer:
Positive charge is found at the upper end of the cumulonimbus clouds.

Question b.
Which type of charge is found at the low end of the cumulonimbus clouds?
Answer:
Negative charge is found at the low end of the cumulonimbus clouds.

Question c.
Which type of charge is found on the land below the cumulonimbus clouds?
Answer:
Positive charge is found on the land below the cumulonimbus clouds.

Use your brainpower!

Find where the symbols given below are used while showing the weather of a place. Write their meanings in the boxes given below:
(Note: The answer is given directly.)

Question a

Answer:

Thought-Provoking Questions:

Think about it.

Question a.
During winters, when you exhale on the glass of your mirror, what happens. If you do this in summer why doesn’t it happen?
Answer:
1. During winters, the moisture-holding capacity of air is low due to low temperature. Therefore during winters, when we exhale on the glass of mirror, the condensation of water vapour present in the exhaled air takes place. As its effect very thin water drops are found on the glass of mirror.

2. During summer, the moisture-holding capacity of air is high due to high temperature. Therefore during summer, when we exhale on the glass of mirror, the water vapour present in the exhaled air gets absorbed in air. Therefore, no water drops are found on the glass of mirror.

Give it a try.

The vapour-holding capacity of 1 cu.m, of air in various temperature is given in the following table.

Calculate the difference in the capacities by observing the following table :
(Note: The answer is given directly.)

Question a.

Answer:

Use your brain power!

Question a.
In which season is humidity generally more?
Answer:
Humidity is generally more in monsoon.

Question b.
How does the humidity affect the human body?
Answer:
The rate of respiration and sweating increases due to humidity.

Question c.
Observe how humidity affects the food materials at our home and write about the same.
Answer:
Due to humidity, fungus flourish on food materials at our home and it gets spoiled.

Question d.
Is there any relationship between formation of fungus and humidity?
Answer:
There is a direct relationship between formation of fungus and humidity. Humidity supports the growth of fungus.

Question e.
How is the early or late drying up of clothes related to humidity?
Answer:
As the moisture-holding capacity is found to be high in low humidity air, it leads to early drying up of clothes. As the moisture-holding capacity is found to be low in high humidity air, it leads to late drying up of clothes.

Think about it.

Question a.
What will happen if the temperature of saturated air at 20° C drops to 10° C abruptly?
Answer:

1. If the temperature of saturated air at 20° C drops to 10° C abruptly, the relative humidity of the air will increase abruptly.
2. Rise in the relative humidity will lead to condensation or sublimation of water vapour in the air. This in turn, will lead to precipitation or snowfall.

Open-Ended Question:

Question a.
Explain the effect of humidity on human life.
Answer:

1. High humidity increases the rate of sweating and respiration. This adversely affects the daily functioning.
2. Low humidity with pleasant atmosphere, have favourable effects on the daily routine.
3. High humidity leads to late drying up of clothes and early spoiling of food materials.
4. Low humidity leads to early drying up of clothes and late spoiling of food materials.