Figure shows a long straight wire of a circular cross-section (radius a) carrying steady current l. The current l is uniformly distributed across this cross-section. Calculate the magnetic field in the region `r lt a and r gt a`

Options

A. `1//4`
B. `4`
C. `1`
D. `1//2`

Answer

3

Explanation

`B_(1)=(mu_(0)i)/(2pia^(2))` where `0lerlea B_(1)=(mu_(0)i)/(2pia^(2))a/2 (at r=a/2)`
`(mu_(0)i)/(4pia^(2)),B_(2)=(mu_(0)i)/(2pi(2a)) (at r=2a) B_(1)/B_(2)=1`