# In the ratio of the concentration of electrons that of holes in a semiconductor is 7/5 and the ratio of currents is 7/4 then what is the ratio of their drift velocities? Option 1) 4/7 Option 2) 5/8 Option 3) 4/5 Option 4) 5/4

As we have learnt,

Electrical Conductivity (σ) -

$\sigma =e \left (n_{e}\mu _{e}+n_{h}\mu _{h} \right )$

- wherein

$n_{e}= electron \: density$

$n_{h}= hole \: density$

$\mu _{e}= mobility \: of \: electron$

$\mu _{h}= mobility \: of \: holes$

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

$I = nv_\alpha eA$

$\\\frac{I_e}{I_h} = \frac{n_ev_{d,e}}{n_h v_{d,h}} \Rightarrow \frac{v_{d,e}}{v_{d,h}} = \frac{I_e}{I_h}\cdot\frac{n_h}{n_e} \\\frac{v_{d,e}}{v_{d,h}} = \frac{7}{4}\times \frac{5}{7} = \frac{5}{4}$

Option 1)

4/7

Option 2)

5/8

Option 3)

4/5

Option 4)

5/4

Exams
Articles
Questions