Sources of Energy NCERT Exemplar Problems
Short Answer
Question 13: In a hydroelectric power plant more electrical power can be generated if water falls from a greater height because
- Its temperature increases
- Larger amount of potential energy is converted into kinetic energy
- The electricity content of water increases with height
- More water molecules dissociate into ions
Answer: (b) Larger amount of potential energy is converted into kinetic energy
Question 14: Choose the incorrect statement regarding wind power
- It is expected to harness wind power to minimum in open space
- The potential energy content of wind blowing at high altitudes is the source of wind power
- Wind hitting at the blades of a windmill causes them to rotate. The rotation thus achieved can be utilised further
- One possible method of utilising the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator
Answer: (b) The potential energy content of wind blowing at high altitudes is the source of wind power
Question 15: Choose the incorrect statement
- We are encouraged to plant more trees so as to ensure clean environment and also provide bio-mass fuel
- Gobar-gas is produced when crops, vegetable wastes etc., decompose in the absence of oxygen
- The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash
- Bio-mass is a renewable source of energy
Answer: (c) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash
Short Answer Questions
Question 16: Why is there a need to harness non-conventional sources of energy? Give two main reasons.
Answer: Two main reasons for harnessing non-conventional sources of energy are as follows:
- Overdependence on fossil fuels
- Increasing pollution in environmental
Question 17: Write two different ways of harnessing energy from ocean.
Answer: Two different ways of harnessing energy from ocean are as follows:
- Tidal Energy
- Ocean Thermal Energy
Question 18: What steps would you suggest to minimise environmental pollution caused by burning of fossil fuels?
Answer: Following steps can be taken to minimize environmental pollution caused by burning of fossil fuels:
- Increase the use of public transport
- Use bicycle for short distance commute
- Develop cleaner sources of energy
Question 19: What is the role of a plane mirror and a glass sheet in a solar cooker?
Answer: The plane mirror in a solar cooker reflects sunlight so that maximum energy is available inside the cooker. The glass sheet creates greenhouse effect by preventing escape of energy from the cooker.
Question 20: Mention three advantages of a solar cell?
Answer: Three advantages of a solar cell are as follows:
- They are non-polluting
- They can be utilized to store solar energy in batteries
- They can be installed even in remote areas
Question 21: What is biomass? What can be done to obtain bio-energy using biomass?
Answer: Plant or animal material used as fuel is called biomass. Biomass can be used in many ways. Cowdung is used for making dried cakes which are used as kitchen fuel. Farm waste can be processed to make biogas which can be used as fuel. Now-a-days, biomass is also utilized to make biodiesel.
Question 22: What are the limitations in obtaining energy from wind?
Answer: Following are the limitations of obtaining energy from wind:
- Wind-farms can be installed only at select locations, where reasonable wind speed is available for most parts of the year.
- Cost of installation of wind mill is very high
- A windmill contains too many rotating parts, which need frequent repair. So, cost of maintenance is also high.