Q. If the ratio of the concentration of electrons to that of holes in a semiconductor is $\frac{7}{5}$ and the ratio of current 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) $\frac{4}{7}$
Explanation
(c) $I = n_{e}{Av}_{d}$
$\frac{I_{e}}{I_{h}} = \frac{n_{e} \times \left( v_{d} \right)_{e}}{n_{h} \times \left( v_{d} \right)_{h}}$
Here,$\ \frac{n_{e}}{n_{h}} = \frac{7}{5},\frac{I_{e}}{I_{h}} = \frac{7}{4}$
$\frac{7}{4} = \frac{7}{5} \times \frac{\left( v_{d} \right)_{e}}{\left( v_{d} \right)_{h}}$
$\Rightarrow \frac{\left( v_{d} \right)_{e}}{\left( v_{d} \right)_{h}} = \frac{5}{7} \times \frac{7}{4} = \frac{5}{4}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.