Drift velocity in a metallic conductor:
At room temperature there are large number of free electrons having zero average velocity, but when electric field is applied, the free electrons start moving in a direction opposite to the direction of the applied field with a velocity called drift velocity.
Mobility of free electron is

Options

A. `(e(tau))/(m_e)`
B. `e/((tau)m_e)`
C. `tau/(em_e)`
D. `m_e/(e(tau))`