# Exercise-6C Heat and Energy Concise Class-9 ICSE Physics Selina Publishers

Exercise-6C Heat and Energy Concise Class-9 ICSE Physics Selina Publishers Solutions Chapter-6 . Step By Step ICSE Selina Concise Solutions of Chapter-6 Heat and Energy  with Exercise-6(A), Exercise-6(B) , Exercise-6(C) and Exercise-6(D) including Numerical and MCQ Questions Solved Visit official Website CISCE for detail information about ICSE Board Class-9.

 Board ICSE Publications Selina Publication Subject Physics Class 9th Chapter-6 Heat and Energy  Exe-6(C) Book Name Concise Topics Solution of Exercise-6(A),  MCQ-6(A) , Exercise-6(B)  MCQ-6(B),  Exercise-6(C)   MCQ-6(C)  and Exercise-6(D),  MCQ-6(D) Academic Session 2021-2022

## Exercise-6C Heat and Energy Concise Class-9 ICSE Physics Selina Publishers

–: Select Topics :–

Exercise-6(A),  MCQ-6(A)

Exercise-6(B)  MCQ-6(B),

Exercise-6(C),  MCQ-6(C)

Exercise-6(D),  MCQ-6(D)

Note :-  Before Viewing Selina Concise Physics Solutions of Chapter-6 Heat and Energy for ICSE Class-9 Physics. Read the whole chapter carefully and Solved all example of Chapter-6 Heat and Energy for Class-9 Physics.

Page 141

#### Question 1

State two characteristics which a source of energy must have.

• A source of energy should be safe and convenient to use.
• A source of energy should be economical and easy to store and transport.

#### Question 2

Name the two groups in which various sources of energy are classified. State on what basis are they classified.

The two groups in which various sources of energy are classified are renewable or non-conventional sources of energy and non-renewable or conventional sources of energy.

These sources are classified on the basis of their availability and utility.

#### Question 3

What is meant by the renewable and non-­renewable sources of energy? State two differences between them, giving two examples of each.

Renewable: The natural sources providing us energy continuously are called renewable sources of energy.

Non-renewable: The sources of energy which have accumulated in nature over a very long period of time and cannot be quickly replaced when exhausted are called non-renewable sources of energy.

Difference:

 Renewable sources Non-renewable sources They can be utilised continuously. They cannot be utilised once exhausted. Examples: Sun, Wind Example: Coal, Petroleum

#### Question 4

Select the renewable and non-renewable sources of energy from the following :

(a) Coal

(b) Wood

(c) Water

(d) Diesel

(e) Wind

(f) Oil

Renewable: Wood, Water and Wind

Non-renewable: Coal, Diesel and Oil

#### Question 5  Exercise-6C Heat and Energy Concise

Why is the use of wood as a fuel not advisable although wood is a renewable source of energy?

Wood is obtained from trees. Hence, trees need to be cut down for wood to be used as a fuel.

Also, burning wood releases a lot of smoke which pollutes the atmosphere.

#### Question 6

Name five renewable and three non-renewable sources of energy.

Renewable:

1. Sun
2. Wind
3. Flowing water
4. Tides
5. Nuclear fuel

Non-renewable:

1. Coal
2. Petroleum
3. Natural gas

#### Question 7

What is (i) tidal, (ii) ocean and (iii) geo thermal energy? Explain in brief.

##### Tidal energy:

The energy possessed by rising and falling water in tides is known as tidal energy. Dams are constructed across a narrow opening to the sea to harness tidal energy and produce electricity. However, it is not a major source of energy as the rise and fall of seawater during tides is not enough to generate electricity on a large scale.

##### Ocean energy:

Water in the oceans possesses energy in two forms:

##### Ocean thermal energy-

The energy available due to the difference in temperature of water at the surface and at deeper levels of ocean is called the ocean thermal energy. This energy is harnessed for producing electricity by a device called ocean thermal energy conversion power plant (OCTEC power plant).

##### Oceanic waves energy-

The kinetic energy possessed by fast moving oceanic (or sea) waves is called oceanic waves energy. Though models have been made to generate electricity from oceanic waves, but so far it has not been put to practical use.

##### Geo thermal energy:

The heat energy possessed by the rocks inside the Earth is called geothermal energy.The hot rocks present at the hot spots deep inside the Earth, heat the underground water and turn it into steam. This steam is compressed at high pressure between the rocks. Holes are drilled deep into the Earth up to the hot spots to extract the steam through pipes, which is utilized to rotate the turbines connected to the armature of an electric generator to produce electricity.

#### Question 8  Exercise-6C Heat and Energy Concise

What is the main source of energy for Earth?

Sun is the main source of energy on Earth.

#### Question 9

What is solar energy? How is the solar energy used to generate electricity in a solar power Plant?

The energy obtained from Sun is called solar energy.

A solar power plant is a device in which heat energy of sun is used to generate electricity. It consists of a large number of concave reflectors, at the focus of which there are black painted water pipes. The reflectors concentrate the heat energy of the sun rays on the pipes due to which water inside the pipes starts boiling and produces steam. The steam thus produced is used to rotate a steam turbine which drives a generator producing electricity.

#### Question 10

What is a solar cell? State two uses of solar cells. State whether a solar cell produces a.c. or d.c. Give one disadvantage of using a solar cell.

A solar cell is an electrical device that converts light energy directly into electricity with the help of photovoltaic effect. Solar cells are usually made from semiconductors like silicon and gallium with some impurity added to it. When sunlight is made incident on a solar cell, a potential difference is produced between its surface, due to which a current flows in the circuit connected between the opposite faces of the semiconductor.

Two uses of solar cells are as listed below:

• They do not require maintenance and last over a long period of time at zero running cost.
• They are very useful for remote, inaccessible and isolated places where electric power lines cannot be laid.Solar cell produces d.c. (direct current).

One disadvantage of solar cell is listed below:

• The initial cost of a solar panel is sufficiently high

#### Question 11

State two advantages and two limitations of producing electricity from solar energy.

1. They do not cause any pollution in the environment.
2. Running cost of solar panel is almost zero.
3. It last over a long period of time.
4. They do not require any maintenance.
5. Solar Energy are suitable for remote and inaccessible places where electricity power lines cannot be laid.

1. The initial cost of a solar panel is sufficiently high.
2. The efficiency of conversion of solar energy to electricity is low.
3. A solar panel produces d.c. electricity which cannot be directly used for many household purposes.

#### Question 12  Exercise-6C Heat and Energy Concise

What is wind energy? How is wind energy used to produce electricity? How much electric power is generated in India using the wind energy?

The kinetic energy of the moving large masses of air is called the wind energy. Wind energy is used in a wind generator to produce electricity by making use of wind mill to drive a wind generator.

At present in India, more than 1025 MW electric power is generated using wind energy.

#### Question 13

State two advantages and two limitations of using wind energy for generating electricity.

• It does not cause any kind of pollution.
• It is an everlasting source.

Limitations of using wind energy:

• The establishment of a wind farm is expensive.
• A large area of land is needed for the establishment of a wind farm.

#### Question 14

What is hydro energy? Explain the principle of generating electricity from hydro energy. How much hydro electric power is generated in India?

The kinetic energy possessed by flowing water is called the water or hydro energy.

Principle of a hydroelectric power plant is that the water flowing in high altitude rivers is collected in a high dam (or reservoir). The water from the dam is then allowed to fall on a water turbine which is located near the bottom of the dam. The shaft of the turbine is connected to the armature of an electric generator or dynamo.

At present only 23% of the total electricity is generated by the hydro energy.

#### Question 15

Advantages of producing the hydro electricity:

1. It does not produce any environmental pollution.
2. It is a renewable source of energy.

1. Due to the construction of dams over the rivers, plants and animals of that place get destroyed or killed.
2. The ecological balance in the downstream areas of rivers gets disturbed.

#### Question 16  Exercise-6C Heat and Energy Concise

What is nuclear energy? Name the process used for producing electricity using the nuclear energy.

When a heavy nucleus is bombarded with slow neutrons, it splits into two nearly equal light nuclei with a release of tremendous amount of energy. In this process of nuclear fission, the total sum of masses of products is less than the total sum of masses of reactants. This lost mass gets converted into energy. The energy so released is called nuclear energy.

##### Principle:

The heat energy released due to the controlled chain reaction of nuclear fission of uranium-235 in a nuclear reactor is absorbed by the coolant which then passes through the coils of a heat exchanger containing water. The water in heat exchanger gets heated and converts into steam. The steam is used to rotate the turbine which in turn rotates the armature of a generator in a magnetic field and thus produces electricity.

#### Question 17

What percentage of total electrical power generated in India is obtained from nuclear power plants? Name two places in India where electricity is generated from nuclear power plants.

At present only about 3% of the total electrical power generated in India is obtained from the nuclear power plants.

Tarapur in Maharahtra and Narora in Uttar Pradesh are the places where electricity is produced using nuclear energy.

#### Question 18

State two advantages and two disadvantages of using nuclear energy for producing electricity.

1. A very small amount of nuclear fuel can produce a tremendous amount of energy.
2. Once the nuclear fuel is loaded into nuclear power plant, it continues to release energy for several years.

1. It is not a clean source of energy because very harmful nuclear radiations are produced in the process.
2. The waste causes environmental pollution.

#### Question 19

State the energy transformation in the following:

i. electricity is obtained from solar energy.

ii. electricity is obtained from wind energy.

iii. electricity is obtained from hydro energy.

iv electricity is obtained from nuclear energy.

i. Light energy into electrical energy

ii. Mechanical energy into electrical energy.

iii. Mechanical energy into electrical energy.

iv. Nuclear energy (or heat energy) into electrical energy.

#### Question 20

State four ways for the judicious use of energy.

Four ways for the judicious use of energy are:

1. The fossil fuels such as coal, petroleum, natural gas should be used only for the limited purposes when there is no other alternative source of energy available.
2. The wastage of energy should be avoided.
3. Efforts must be made to make use of energy for community or group purposes.
4. The cutting of trees must be banned and more and more new trees must be roped to grow.

#### Question 21  Exercise-6C Heat and Energy Concise

What do you mean by degradation of energy? Explain it by taking two examples of your daily life.

The gradual decrease of useful energy due to friction etc. is called the degradation of energy.

Examples:

1. When we cook food over fire, the major part of heat energy from the fuel is radiated out in the atmosphere. This radiated energy is of no use to us.
2. When electrical appliances are run by electricity, the major part of electrical energy is wasted in the form of heat energy.

#### Question 22

The conversion of part of energy into a non-useful form of energy is called………

The conversion of part of energy into a non-useful form of energy is called degradation of energy.

Page 141

#### Question 1

The ultimate source of energy is :

(a) wood

(b) wind

(c) water

(d) sun

The ultimate source of energy is the Sun.

#### Question 2

Renewable source of energy is :

(a) coal

(b) fossil fuels

(c) natural gas

(d) sun