If the ratio of the concentration of electrons and that of holes in a semiconductor is 7/5 and the ratio of their currents is 7/4, then the ratio of their drift velocities is

Options

A. `5//8`
B. `4//5`
C. `5//4`
D. `4//7`

Answer

C

Explanation

`I=n_(e) Av_(d)`
`(I_(e))/(I_(h))=(n_(e)xx(v_(d))_(e))/(n_(h)xx(v_(d))_(h))`
Here `(n_(e))/(n_(h))=7/5 xx((v_(d))_(e))/((v_(d))_(h))=(7)/(4)`
`(7)/(4) = (7)/(5) xx((v_(d))_(e))/((v_(d))_(h))`
`rArr ((v_(d))_(e))/((v_(d))_(g))=5/7xx7/4 =5/4`