Give two merits of solar cells.

What are fossil fuels? Name any three fossil fuels.

$(i)$ Distinguish between renewable and non-renewable sources of energy,giving one example of each.
$(ii)$ Why is the use of wood as a fuel not advised,although forests can be replenished?

$(a)$ 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?

State whether the following statement is true or false:
Solar energy has the greatest potential of all the renewable sources of energy.

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