Which is the ultimate source of energy?

Name the agent which decomposes animal dung into biogas. Describe the steps involved in the process.

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?

What prevents us from making use of solar cell panels to meet all our domestic needs for electricity?

State any two impacts on the environment caused due to the increase in energy demand. Suggest any two steps to reduce energy consumption.

The longest and the shortest wavelengths (in $\mu m$) for red and violet light are respectively: