Question

If the ratio of the concentration of electron to that of holes in a semiconductor is `(7)/(5)` and the ratio of current is `(7)/(4)` then what is the ratio of their drift velocities ?
A. `5//8`
B. `4//8`
C. `5//4`
D. `4//7`

Answer 1

Correct Answer - C
`I=n eAv_(d)`
`(I_(e))/(I_(h))=(n_(e)xx(v_(d))_(e))/(n_(h)xx(v_(d))_(h))`
Here `(n_(e))/(n_(h)) = (7)/(5), (I_(e))/(I_(h)) = (7)/(4)`
`:. (7)/(4) =(7)/(5)xx((v_(d))_(e))/((v_(d))_(h))`
`rArr ((v_(d))_(e))/((v_(d))_(h))=(5)/(7)xx(7)/(4)=(5)/(4)`.