Mention any two advantages and two disadvantages of producing hydroelectricity by building dams on rivers.

Name any two materials that are used to make solar cells.

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

What are the environmental consequences of using fossil fuels? Suggest the steps to minimize the pollution caused by various sources of energy,including non-conventional sources of energy.

$(a)$ 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?

The temperature difference required up to a water level difference of $1000 \,m$ for operating an Ocean Thermal Energy Conversion $(OTEC)$ system is: (in $^{\circ} C$)