Question

Define mobility of a charge carrier. What is its relation with relaxation time?

Answer 1

The mobility of a charge carrier is defined as the drift velocity of the charge carrier per unit electric field.

Thus, mobility , $\mu =\frac{v_d}{E}$

If $q$ be the charge of carrier and $\tau$ be the relaxation time, then mobility $\mu =\frac{q\tau }{m}$ where $m$ be the mass of the charge carrier.