An electric cell of e.m.f E is connected across a copper wire of diameter d and length l. The drift velocity of electrons in the wire is `v_(d)`. If the length of the wire is changed to 2l, the new drift velocity of electrons in the copper wire will be

Options

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

Answer

C

Explanation

`I = "ne"Av_(d) = v_(d) = I/("ne"A) = (IR)/("ne"AR) = V/("ne"A(rhol)/A)`
`rArr v_(d) = V/("ne"rhol) rArr v_(d) prop 1/l`
If `l. to 2l`, then `v_(d) rArr v_(d)//2`