NCERT Solutions Execise 

Q1. A solar water heater cannot be used to get hot water on

(a) a sunny day.

(b) a cloudy day.

(c) a hot day. 

(d) a windy day.

Ans: (b) a cloudy day.

Q2. Which of the following is not an example of a bio-mass energy source?

(a) wood

(b) gobar-gas

(c) nuclear energy

(d) coal

Ans: (c) nuclear energy

Q3. Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy? (a) geothermal energy

(b) wind energy

(c) nuclear energy

(d) bio-mass.

Ans: (c) nuclear energy

Q4. Compare and contrast fossil fuels and the Sun as direct sources of energy.

Ans:

fossil fuels:

(i) It is terminating.

(ii) It is an expensive source of energy.

(iii) They also affect the greenhouse.

  Sun :

(i) It is not tenable.

(ii) It is a cheap source of energy.

(iii) This equipment is a source of clean energy.

Q5. Compare and contrast bio-mass and hydro electricity as sources of energy.

Ans: 

Biomass :

(i) It is a renewable source of energy.

(ii) Its cost is not high.

(iii) is due to the generation of bio gas.

Hydroelectricity:

(i) It is also a renewable source of energy.

(ii) Hydroelectricity is generated from water.

(iii) Its cost is expensive to some extent.

Q6. What are the limitations of extracting energy from—

(a)the wind?

(b) waves?

(c) tides?

Ans: (a) Winds :

(i) The energy from the winds is found in those places where the wind blows at a high speed during the rainy season.

(ii) For the speed of turbines, the minimum speed of the wind should be more than 15 km/h.

(iii) Auxiliary cells should also be available for its use.

(b) Waves :

(i) The waves must be strong to get the energy generated by the waves

(ii) The same electric power cannot be obtained while using it.

(iii) The equipment required for this is expensive.

(c) Tidal :

(i) It is necessary to build a dam to get this kind of energy.

(ii) The use of energy generated by tides is limited.

(iii) The cost of land for its construction is high.

Q7. On what basis would you classify energy sources as

(a) renewable and non-renewable?

(b) exhaustible and inexhaustible?

Are the options given in (a) and (b) the same?

Ans: 

(a) Renewable energy is the energy which we can use indefinitely for a long time. Its reserves remain renewable. Eg: Solar power and wind power.

 Non-renewable energy is the energy which if we use it once, it cannot be recovered and its reserves remain exhausted. Such as: fossil fuels (coal, petrol, natural gas).

(b) The options for (a) and (b) are the same because renewable energy is renewable but non-renewable energy is non-renewable.

Q8. What are the qualities of an ideal source of energy?

Ans: Characteristics of an ideal source of energy:-

(i) can be easily obtained.

(ii) should also be cheap.

(iii) do more work per unit volume and mass.

Q9. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

Ans: Benefits of using solar cooker:

(i) This equipment is cheap.

(ii) There is no pollution by using it.

(iii) They do not have any moving parts.

Disadvantages of Solar Cooker:

(i) This device is used only in sunlight.

(ii) It takes more time to cook food.

   Yes, there are many such areas. Solar-cells are expensive. Where solar cookers have limited utility eg: areas with high rainfall, hilly areas etc.

Q10. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

Ans: Today's era has become a mechanical age, today's population uses fossil fuels to pollute the environment. Environmentally friendly using solar cells. Many types of diseases are increasing.

  Following are the measures to reduce energy consumption:

(i) Least use of coal, fossil fuel.

(ii) Relying on oneself instead of relying on machines.