During the formation of a $$p$$-$$n$$ junction:

Assertion (A) : The resistance of an intrinsic semiconductor decreases with increase in its temperature.

Reason (R) : The number of conduction electrons as well as hole increase in an intrinsic semiconductor with rise in its temperature.

In an extrinsic semiconductor, the number density of holes is $$4 \times 10^{20} \mathrm{~m}^{-3}$$. If the number density of intrinsic carriers is $$1.2 \times 10^{15} \mathbf{m}^3$$, the number density of electrons in it is

Pieces of copper and of silicon are initially at room temperature. Both are heated to temperature T. The conductivity of