• # question_answer     The ratio of electron and hole currents in a semiconductor is 7/4 and the ratio of drift velocities of electrons and holes is 5/4 then ratio of concentrations of electrons and holes will be A)  5/7                                        B)  7/5 C)  25/49                                    D)  49/25

$I=n\,A\,e\,{{v}_{d}}$or$I\propto n{{v}_{d}}$ $\therefore$  $\frac{{{I}_{e}}}{{{I}_{h}}}=\frac{{{n}_{e}}{{V}_{e}}}{{{n}_{h}}{{v}_{h}}}$ Or           $\frac{{{n}_{e}}}{{{n}_{h}}}=\frac{{{I}_{e}}}{{{I}_{h}}}=\frac{{{v}_{h}}}{{{v}_{e}}}$                 $=\frac{7}{4}\times \frac{4}{5}=\frac{7}{5}$