Question

Define resistivity of a conductor. How does the resistivity of a conductor depend upon the following : (a) Number density of free electrons in the conductor (n) (b) Their relaxation time (τ)

What is meant by 'relaxation time' of free electrons in a conductor ? Show that the resistance of a conductor can be expressed by R = ml/(ne²τA), where symbols have their usual meanings.

Draw the circuit diagram of a Wheatstone bridge. Obtain the condition when no current flows through the galvanometer in it.

Assertion (A) : When electrons drift in a conductor, it does not mean that all free electrons in the conductor are moving in the same direction. Reason (R) : The drift velocity is superposed over large random velocities of electrons.