When a current I is set up in a wire of radius r, the drift velocity is `v_(d)`. If the same current is set up through a wire of radius 2r, the drift speed will be

Options

A. `0.25 v_(d)`
B. `0.5 v_(d)`
C. `2 v_(d)`
D. `4 v_(d)`

Answer

A

Explanation

`v_(d) prop(1)/(r^(2)) :. V_(d1)r_(1)^(2)=v_(d2)r_(2)^(2)`
`:.v_(d2)=((r_(1))/(r_(2)))^(2) v_(d1)= ((r)/(2r))^(2) vd=0.25 v_(d)`