Question

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.

Assertion (A) : The temperature coefficient of resistance is positive for metals and negative for semi-conductors. Reason (R) : The charge carriers in metals are negatively charged whereas in semiconductors they are positively charged.

Derive the relation between the current and the drift velocity of free electrons in a conductor. Briefly explain the variation of resistance of a conductor with rise in temperature.

An ammeter, together with an unknown resistance in series is connected across two identical batteries, each of emf 1·5 V, connected (i) in series, and (ii) in parallel. If the current recorded in the two cases be (1/2) A and (1/3) A respectively, calculate the internal resistance of each battery.