Justify in one sentence that hydro power (hydro electricity) is a renewable source of energy.

Name any two devices used to harness solar energy.

In parabolic reflector type cookers, even temperature up to 1800^oC-2000^o can be attained. How?

What type of energy transformation takes place during winding of spring of a clock?

In many applications, solar cells are connected to rechargeable batteries. Why is it so?

How is the increase in demand for energy affecting our environment adversely?

How were fossil fuel formed?

Name four gases commonly present in biogas. State two advantages of using this gas over fossil fuels.

Of the major requirement of different forms of energies, write which one is the greater requirement of India and which is the least? What is the percentage of the hydro energy requirement of India?

For producing electricity, the energy from flowing water is preferred to energy obtained by burning coke. State two reasons for it.

Give a few examples of how our ancestors used the energy possessed by the wind and water.

Out of two solar cookers, one was covered by a plane glass slab and the other was left open. Which of the two solar cookers will be more efficient and why?

people living on hills often get sunburns on their skin. Which component of sunlight is responsible for this effect? Why is this effect generally not observed near sea level?

A certain form of energy which is not sourced directly or indirectly from the sun and does not cause any pollution is very easily converted into electricity. This form of energy is however, not available everywhere. Moreover, it is technically very difficult and expensive to obtain it. Name the form of energy.

Why any source of energy has less consequence? Explain your answer with suitable example.

what is the cause of release of unusually large energies in nuclear fission reactions? How is the energy per fission calculated?

The solar constant at a place is 1.4 kW/m². How much will solar energy be received at this place per second over an area of 5 m²?

What is the basic cause for winds to blow? Name a part of India, where wind energy is commercially harnessed. Compare wind power and power of water flow in respect of generating mechanical and electrical energies. What is the hindrance in developing them?

A certain form of energy is available due to the difference in the temperature of water at the surface of the ocean and its deeper levels.

(i) Name the form of energy.

(ii) Is this energy ultimately derived from the sun or not?

(iii) Explain, how this form of energy can be converted into electricity?

Nikhil and Neha went to a remote village in Kerala to meet their grandmother. They were surprised to see bio-gas plant in Mr. Nair’s house in the neighborhood. There was plenty of livestock and the house hold use cooking gas from the plant. Also, their farm had rich vegetation. They contacted sarpanch of the village and convinced him to set up a bio-gas plant for village community.

(i) Mention the values displayed by Mr. Nair. Nikhil and Neha.

(ii) Explain the possible arguments given by Nikhil and Neha to the sarpanch to convince him to set up a bio-gas plant.

Hemant visited his neighboring village, where a bio-gas plant has been installed recently. He was surprised to see the working of the bio-gas plant. He told his village elders about the advantages of setting up a bio-gas plant in their village. Now. Answer the following question:

(i) What are the advantages of a biogas plant?

(ii) Why is a bio-gas plant commonly called as gobar gas plant?

(iii) Why were the villagers are very much impressed with Hemant?