Question

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

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

Answer 1

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

Now, $I=n{q}_{e}A{v}_d$

$\Rightarrow \frac{I_e}{I_h}=\frac{n_e\times (v_d{)}_e}{n_h\times (v_d{)}_h}$

Here, $\frac{n_e}{n_h}=\frac{7}{5},\frac{I_e}{I_h}=\frac{7}{4}$

$\frac{7}{4}=\frac{7}{5}\times \frac{(v_d{)}_e}{(v_d{)}_h}$

$\Rightarrow \frac{(v_d{)}_e}{(v_d{)}_h}=\frac{5}{7}\times \frac{7}{4}=\frac{5}{4}$

Hence, $\left(C\right)$ is the correct answer.