Question

a wire of &
A flows through
diameter 20 mm. Calculate the cennent density.
A cunnent of 12x10-10​

Answer 1

Explanation:

The current I in the uniform wire of diameter d1 i.e. 

radius r1 with mean electron drift velocity v1 is given by,

I=ne4π(r1)2v1

if the same current flows through the wire of diameter 2d1 i.e radius 2r1 with drift velocity v2 is given by 

I=ne4π(2r1)2v2

Therefore we can write

I=ne4π(r1)2v1=ne4π(2r1)2v2

⇒v1=4v2

∴v2=4v1