Name any two materials that are used to make solar cells.

Why is the use of biomass to generate heat:
$(i)$ discouraged by burning it directly in ovens (chulhas),and
$(ii)$ encouraged for obtaining biogas through a biogas plant?

Choose the only renewable source of energy from the following:

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?

$A$ student constructed a box-type solar cooker. He found that it did not work efficiently. Give any four possible mistakes in the construction and operation of the solar cooker.

What are the causes of acid rain?