Derive an expression of drift velocity and write the relation between drift velocity and mobility.

Explanation

The drift velocity is the average acquired by the electrons inside the conductor when it is subjected to an electric field. The average time between successive collisions is called the mean free time denoted by `tau`. The acceleration `veca` experiences by the electron in an electric field `vec E` is given by
`vec a=(- vec evecE)/(m) ("since" vec F =- c vec E)`
The drift velocity is given by
`vec v_(d)=veca tau`
`vecv_(d)=-(e tau)/(m) vecE`
`vecv_(d)=mu vec E`
Here `mu=(e tau)/(m)` is the mobility of the electron and it is defined as the magnitude of the dricft velocity per unit electrod field.
`mu=(|vec vd|)/(|vec E|)`