A conductor wire having `10^29` free electrons `/ m^3` carries a current of 20A. If the cross-section of the wire is `1mm^2`, then the drift velocity of electrons will be :

Options

A. `1.25xx10^(-4)ms^(-1)`
B. `1.25xx10^(-3)ms^(-1)`
C. `1.25xx10^(-5)ms^(-1)`
D. `6.25xx10^(-3)ms^(-1)`

Answer

B

Explanation

Here, `I=20 A,n=10^(29)m^(-3)`
`A=1mm^(2)=10^(-6)m^(2),e=1.6xx10^(-19)C`
Drift velocity, `v_(d)=(I)/(nAe)`
`=(20A)/(10^(29)m^(-3)xx10^(-6)m^(2)xx1.6xx10^(-19)C)=1.25xx10^(-3)ms^(-1)`