Question

The mobility of free electrons (charge= e, mass= m and relaxation time = $\tau$) in a metal is proportional to

• A. $\frac {e}{m}\tau$
• B. $\frac {m}{e}\tau$
• C. $\frac {e}{m\tau}$
• D. $\frac {m}{e\tau}$

Answer 1

Answer: (A)

$\frac {e}{m}\tau$

Answer 2

Drift velocity per unit electric field is called mobility of electron $ie, \mu = \frac {v_d}{E} = \frac {E}{\rho neE}$ Now, $\, \, \, \, \, \, \, \rho = \frac {m}{ne^2 \tau}$ $\therefore \, \, \, \, \, \, \, \, \, \mu = \frac {ne^2 \tau}{mne} = \frac {e \tau}{m}$