Give two examples of fossil fuels.

Which is the ultimate source of energy?

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

$(a)$ Why is the solar cooker box covered with a plane glass plate?
$(b)$ Why is energy of water flowing in a river considered to be an indirect form of solar energy?
$(c)$ How is the fission of ${}^{235}U$ nucleus brought about?

Mention three advantages of a solar cell.

$(i)$ Write the value of the solar constant of the Sun.
$(ii)$ What type of mirror is used in a box-type solar cooker?
$(iii)$ Why is it difficult to use hydrogen as a source of energy?
$(iv)$ What is the maximum temperature attained in a concave reflector-type solar cooker?
$(v)$ Fossil fuels are classified as a non-renewable source of energy. Explain why.