The main constituent of biogas is

Aditya suggests his family to install a solar water heater at their residence. But some of the family members were in favour of installing an electric geyser.
$(a)$ Who,according to you,is taking a correct decision? Mention the value exhibited by Aditya.
$(b)$ Also,give reasons (at least $2$) for your answer.

With the help of a labelled diagram,explain the construction and working of a solar water heater.

Which elements are used to make a solar cell?

Why is tidal energy not likely to be a potential source of energy?

State whether the following statement is true or false:
Black surfaces are poor absorbers of heat.