Define relaxation time of the free electrons drifting in conductor. How is it related to the drift velocity of free electrons? Use this relation to deduce the expression for the electrical resistivity of the material.

Explanation

Relaxation time : The time of free travel of electrons between successive collisions is called the relaxation time. It is denoted by `tau.`
when temperature increases, the thermal speed of electrons increases, so collisions of electrons occur more frequently. As a result, the relaxation time decreases of temperature. Relaxation between resistivity and relaxation time is
`rho=(M)/(n e^(2)tau).`