Question

A current 4.0 A exist in a wire of cross-sectional area `2.0 mm^(2)`. If each cubic metre of the wire contains `12.0xx10^(28)` free electrons, then the drift spped is
A. `6.0xx10^(28) m^(-3)`
B. `3.6xx10^(29) m^(-3)`
C. `7.0xx10^(30) m^(-3)`
D. `8.2xx10^(32) m^(-3)`

Answer 1

Correct Answer - A
We know that, the current of the wire,
`i="neAv"_(d)`
`rArr " " 4=nxx1.6xx10^(-19)xx2xx10^(-6)xx2.1xx10^(-4)`
The number of free free electrons
or `n=6.0xx10^(28)m^(-3)`