NCERT Class X Science Class: Chapter –14. Sources of Energy – Part-3

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Question 13:

In a hydroelectric power plant more electrical power can be generated if water falls from a greater height because

(a) Its temperature increases

(b) Larger amount of potential energy is converted into kineticenergy

(c) The electricity content of water increases with height

(d) More water molecules dissociate into ions

Answer: B

Image Upper and lower reservoir

Image Upper and Lower Reservoir

Image Upper and lower reservoir

Question 14:

Choose the incorrect statement regarding wind power

(a) It is expected to harness wind power to minimum in open space

(b) The potential energy content of wind blowing at high altitudesis the source of wind power

(c) Wind hitting at the blades of a windmill causes them to rotatethe rotation thus achieved can be utilized further

(d) One possible method of utilizing the energy of rotationalmotion of the blades of a windmill is to run the turbine of anelectric generator

Answer: B

Question 15:

Choose the incorrect statement

(a) We are encouraged to plant more trees so as to ensure cleanenvironment and also provide bio-mass fuel

(b) Goober-gas is produced when crops, vegetable wastes etc.,decompose in the absence of oxygen

(c) The main ingredient of bio-gas is ethane and it gives a lot ofsmoke and also produces a lot of residual ash

(d) Bio-mass is a renewable source of energy

Answer: C

Short Answer Questions

Question 16:

Why is there a need to harness non-conventional sources of energy? Give two main reasons.


There is need to harness non conventional source of energy because

1. Conventional sources are going to depleted soon if they are exploited rapidly. Hence, alternative sources of energy is necessary

2. Also to cater the rising demand, it is mandatory to look upto the non conventional sources of energy.

Question 17:

Write two different ways of harnessing energy from ocean.


The energy can be harnessed from ocean in the following ways:

Tidal energy:

Image Tidal energy

Image Tidal Energy

Image Tidal energy

Due to the gravitational pull mainly of the moon on the spinning of the earth, the level of water in the sea rises and falls are called high and low tides that can be harnessed by constructing a dam across a narrow opening to the sea.

Ocean thermal energy:

Image Ocean thermal energy

Image Ocean Thermal Energy

Image Ocean thermal energy

The water at the surface of the sea or ocean is heated by the sun while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy in ocean thermal energy conversion plants.

Question 18:

What steps would you suggest to minimize environmental pollution caused by burning of fossil fuels?


Steps to minimize the pollution are:

(i) The pollution caused by burning fossil fuels can be reduced by increasing the efficiency of the combustion process and using various techniques to produce the smokeless appliances.

(ii) The air pollution caused by burning of coal or petroleum products can be reduced by afforestation.

(iii) The planned and judicious use of energy can minimize the pollution, e.g. use of Liquid Petroleum Gas (LPG) as domestic fuel and Compressed Natural Gas (CNG) in transportation vehicles.

Question 19:

What is the role of a plane mirror and a glass sheet in a solar cooker?


Image Role of a plane mirror and a glass sheet in asolar cooker

Image Role of a Plane Mirror and a Glass Sheet in Asolar Cooker

Image Role of a plane mirror and a glass sheet in asolar cooker

The plane mirror is used in a solar cooker, because it reflects the most of the light falls on it.

A glass sheet is used in a solar cooker because the sun rays pass through the glass sheet cover and get absorbed inside the cooker box. It traps more and more heat rays of the sun, thus heating the food item.