What is geothermal energy?

Explain how hydroelectricity is produced.

What do you suggest to overcome the problem of "limitation of sources of energy"? Mention any three suggestions for the effective use of energy.

Ranvir lives in a village and uses wood as a fuel. He studied in his school that charcoal is a better fuel than wood. He decided to use charcoal instead of wood.
$(a)$ How can Ranvir obtain charcoal from wood?
$(b)$ Why is charcoal considered a better fuel than wood? (Give two reasons)

Solar cooker takes more time as compared to the $LPG$ to boil potato or rice,yet Kunal uses solar cooker for such type of cooking:
$(a)$ Why does Kunal use solar cooker instead of $LPG$? Give reason for your answer.
$(b)$ Name the phenomenon which is responsible for obtaining high temperature in solar cooker?
$(c)$ What is the motivation behind using solar cooker?

Hydroelectricity generated at a dam may be considered to be another form of solar energy. Why?