CBSE Class 10 Science Sources of Energy Assignment Set B

Question. Fill in the blanks

(a) The natural gas consists mainly of ............... .
(b) ................ energy is the heat energy from hot rocks present inside the earth.
(c) The minimum speed of wind necessary for working of a wind generator is .............. .
Answer : (a) Methane, (b) Geothermal, (c) 15 km/h.

Assertion and Reasoning Based Questions
Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If assertion is false but reason is true.

Question. Assertion : Heavy water and Graphite Rod are used as moderators in nuclear reactor.
Reason : It decelerates the fast-moving neutrons to control the chain reaction in the reactor.
Answer : (a)

Question. Assertion : Storage of water in reservoirs for hydropower plants cause socioeconomic problems.
Reason : Rotting of vegetation under anaerobic conditions causes harmful greenhouse methane gas
Answer : (a) 

Question. Assertion : Burning of fossil fuel has more advantages since it gives a lot of energy.
Reason : Results in the scarcity of fossil fuels and increased pollution levels.
Answer : (b) 

Question. Assertion : The efficiency of solar heating devices is much higher than the efficiency of electric heating devices.
Reason : The element which can be used to make solar cells is silicon.
Answer : (d) 

Question. Assertion : In a solar water heater, the outer surface of the copper pipe is painted in black which is fixed in the form of a coil in a box.
Reason : Bending copper pipe as a coil helps to increase the surface area for heating.
Answer : (a)

Question. What is a chain reaction ?
Answer : A reaction in which the particle which initiates (starts) the reaction is also produced during the reaction to carry on the reaction further and further is called a chain reaction.

Question. Why geothermal energy is called a renewable source of energy ?
Answer : Geothermal energy is a renewable source of energy because it will be available for a long time and heat is continuously produced inside the earth.

Question. What is the use of the black painted surface in solar heating devices ?
Answer : Black colour is a very good absorber of heat but a very poor reflector. So, it is used to absorb the maximum amount of heat from the sunlight. It is used in solar heating devices to maximise the absorption of heat and to minimize heat loss due to reflection.

Question. What is the importance of the digester of a biogas plant ?
Answer : The digester of a biogas plant is a sealed chamber in which anaerobic micro-organisms that do not require oxygen decompose or break down complex compounds of the cow-dung slurry.

Question. Bio-gas is also known as gobar gas. Justify.
Answer : Starting material for biogas is mainly cow-dung. So, it is also known as gobar gas.

Question. List three environmental consequences of using fossil fuels. Suggest three steps to minimise the pollution caused by various energy sources. 
Answer : The combustion of fossil fuels releases different harmful products. Three environmental consequences of using fossil fuels are :
(a) It releases CO₂ which is a greenhouse gas which traps the solar energy falling on earth and it leads to global warming.
(b) Carbon monoxide is poisonous gas which when enters in the blood stream stops the functioning of red blood cells to carrying oxygen from lungs to other parts of the body. It also causes death.
(c) Sulphur dioxide released during the burning of fossil fuels is harmful for lungs and causes bronchitis and other diseases.
Steps to minimise the pollution caused by various energy sources are :
(a) Solar cookers should be used to cook food wherever possible.
(b) Use of biogas as domestic fuel should be encouraged in rural areas.
(c) Three R’s strategy–Reduce, Reuse and Recycle should be practiced.

Question. Compare and contrast fossil fuels and the Sun as direct sources of energy. 
Answer : Fossil fuels are non-renewable energy sources and directly available to human beings for use. Hence, fossil fuels are the direct source of energy. These are limited in amount. Fossil fuels take millions of years for their formation. Fossil fuels are also very costly.
On the other hand, sun is a renewable and direct source of energy. Solar energy is available free of cost to all in unlimited amount for billions of years.

Question. Compare and contrast biomass and hydroelectricity as sources of energy.
Answer : (a) Hydroelectricity is generated using the kinetic energy from moving water, while the energy from biomass is generated by decomposition of farm waste.
(b) Biomass is composed of organic compounds so, energy from biomass results in air pollution whereas hydroelectricity causes less pollution as compared to it.

Question.Give reason : “A car parked in sunlight remains hot from inside even when there is no sunlight in the car”.
Answer : The glass windows have the ability to pass the radiations which have wavelength near to the visible light or shorter wavelength. It does not allow infra-red radiations of higher wavelength. However, the sun sends infrared radiations of lower wavelength which pass through the glass windows and gets trapped inside the car as heat. This heat does not pass out of the car and remains inside the car for longer time.

Question. Give the names of two energy sources that you consider to be exhaustible. Give reason for your choices.
Answer : Two exhaustible energy sources are as follows :
Coal : It is produced from dead remains of plants and animals that remain buried under the earth’s crust for millions of years. It takes millions of years to produce coal. Industrialisation has increased the demand of coal. However, coal cannot replenish within a short period of time. Hence, it is a non-renewable or exhaustible source of energy.
Wood : It is obtained from forests. Deforestation at a faster rate has caused a reduction in the number of forests on the earth. It takes hundreds of years to grow a forest. If deforestation is continued at this rate, then there would be no wood left on the earth. Hence, wood is an exhaustible source of energy.