Find below the NCERT Exemplar problems and their solutions for Class 10 Science Chapter, Sources of Energy:

Short Answer Type Questions

Question 16. Why is there a need to harness non-conventional sources of energy? Give two main reasons.

Answer.

The two main reasons to harness non-conventional sources of energy are:

(i) The population of the world is increasing at a very rapid rate due to which demands for energy is increasing day by day.

As, fossil fuels like coal, petroleum, are present in a limited amount which and are likely to finish one day so the need for alternative sources of energy is essential.

(ii) Use of conventional sources of energy (coal, petroleum etc.) causes pollution. To reduce pollution use of non-conventional sources of energy is essential.

Question 17. Write two different ways of harnessing energy from ocean.

Answer.

Two different ways of harnessing energy from ocean are:

• Tidal energy: Due to the gravitational pull of mainly the moon on the spinning earth, the level of water in the sea rises and falls. This phenomenon is called high and low tides and the difference in sea-levels gives us tidal energy. Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.
• 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. These plants can operate if the temperature difference between the water at the surface and water at depths up to 2 km is 20 K (20°C) or more. The warm surface-water is used to boil a volatile liquid like ammonia. The vapours of the liquid are then used to run the turbine of generator. The cold water from the depth of the ocean is pumped up and condense vapour again to liquid.

• Question 18. What steps would you suggest to minimize environmental pollution caused by burning of fossil fuels?

  Answer.

  Environmental pollution caused by burning of fossil fuels can be minimized:

  • By increasing the efficiency of the combustion process and using various techniques to reduce the escape of harmful gases and ashes into the surroundings.
  • By using cleaner fuels like CNG, LPG, etc. which do not produces smoke and ash on combustion.
  • By using public transport & bi-cycles.
  • By using non-conventional sources of energy like solar energy, wind energy etc.

  Question 19. What is the role of a plane mirror and a glass sheet in a solar cooker?

  Answer.

  The plane mirror focuses the sun rays into solar cookers with which it achieve higher temperature.

  The transparent glass sheet kept over the open end of cooker trap the incoming heat radiation (infrared rays) and does not allow them to escape to the surroundings in other words glass sheet act as green house effect.

  Question 20. Mention three advantages of a solar cell.

  Answer.

  Three advantages of a solar cell are:

  (i) Solar cell does not produce any sort of pollution.

  (ii) Solar cell does not require any running costs as it uses sunlight for production of electricity.

  (iii) Solar cell do not have any moving parts hence, making its maintenance cost to be negligible.

  Question 21. What is bio-mass? What can be done to obtain bio-energy using biomass?

  Answer.

  Biomass refers to those living and non-living organic materials that can be used as sources of energy in the form of fuel. Some examples of biomass fuels are biogas, wood, crops, and organic garbage. The chemical energy in biomass is released as heat on burning.

  Bio-energy can be obtained from biomass by following ways:

  • Cow-dung and various plant materials like the residue after harvesting the crops, vegetable waste and sewage are decomposed in the absence of oxygen to give bio-gas. As the starting material is mainly cow-dung, it is popularly known as ‘gobar-gas’.
  • When wood is burnt in a limited supply of oxygen, water and volatile materials present in it get removed and charcoal is left behind as the residue. Charcoal burns without flames, is comparatively smokeless and has a higher heat generation efficiency.

  Question 22. What are the limitations in obtaining energy from wind?

  Answer.

  Limitations in obtaining energy from wind are as follows

  • Wind energy farms can be established only at those places where wind blows for the greater part of a year.
  • The wind speed should also be higher than 15 km/h to maintain the required speed of the turbine.
  • There should be some back-up facilities (like storage cells) to take care of the energy needs during a period when there is no wind.
  • Establishment of wind energy farms requires large area of land. For a 1 MW generator, the farm needs about 2 hectares of land. The initial cost of establishment of the farm is quite high.
  • The tower and blades are exposed to the vagaries of nature like rain, Sun, storm and cyclone, hence, they require a high level of maintenance.