Which process is used to harness nuclear energy these days? Explain it briefly.

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

Give one example each for renewable and non-renewable sources of energy.

There are about $50$ teachers in a school and most of them come to school by their own cars. Many of the teachers come from the same place but everyone prefers to come to school by his/her own car.
Answer the following questions based on the above information:
$(a)$ Do you think that their practice of commuting to school is environmental-friendly? Give one suggestion. Justify your answer.
$(b)$ In what other two ways can we become environmental-friendly?

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

Why are solar heating devices painted black from inside?