Question

If the ratio of the concentration of electron to that of holes in a semiconductor is $\frac{7}{5}$ and the ratio of currents is $\frac{7}{4}$, then what is the ratio of their drift velocities-

• A. $\frac{5}{4}$
• B. $\frac{4}{7}$
• C. $\frac{5}{8}$
• D. $\frac{4}{5}$

Answer 1

The correct option is A $\frac{5}{4}$

By current density,
$I=neA{V}_d$
$\frac{I_e}{I_h}=\frac{n_e\times (V_d{)}_e}{n_h\times (V_d{)}_h}$
where $(V_d{)}_e$ = drift velocity of electron
$(V_d{)}_h$ = drift velocity of hole
$I_h$ = hole current
$I_e$ = electron current
Put the values,
$\Rightarrow \frac{7}{4}=\frac{7}{5}\times \frac{(V_d{)}_e}{(V_d{)}_h}$
$\Rightarrow \frac{(V_d{)}_e}{(V_d{)}_h}=\frac{5}{7}\times \frac{7}{4}=\frac{5}{4}$