A long, straight wire of radius R carries a current distributed uniformly over its cross section. The magnitude of the magnetic field is

Options

A. (i),(ii)
B. (ii),(iii)
C. (i),(iii)
D. (i),(iv)

Answer

B

Explanation

`r lt R: B=(mu_(0)Ir)/(2piR^(2)), (B propr)`
`r lt R: B=(mu_(0)I)/(2piR), (B prop1/r)`
`r = R: B=(mu_(0)I)/(2piR)=B_(max)`