Name the chief component of solar cells. What energy conversion takes place in a solar cell?

Compare the energy produced during the fission of a uranium atom with the energy produced due to the combustion of a carbon atom from coal.

Mention the minimum wind velocity required for obtaining electric power with a windmill generator.

What do you mean by 'ocean thermal energy'? How can electricity be generated from this energy?

Which gas is present both in natural gas and biogas?

$(a)$ Magnetic field lines of two bar magnets $A$ and $B$ are as shown below. Name the poles of the magnets facing each other.
$(b)$ Two magnetic field lines never intersect each other. Why?
$(c)$ How does the strength of the magnetic field at the centre of a current-carrying circular coil depend on the
$(i)$ radius of the coil,
$(ii)$ number of turns in the coil, and
$(iii)$ strength of the current flowing in the coil?