A current i is unifromly distributed over the cross section of a long hollow cylindrical wire o finner radius `R_(1)` and outer radius `R_(2)`. Magnetic field B varies with distance r from the axis of the cylinder as .

Options

A.
B.
C.
D.

Answer

B

Explanation

(b) Using Ampere's circuital law, `B=0 for rleR_`
`B=(mu_0i)/(2pi(R_2^2-R_1^2)) ((r^2-R_1^2)/r) for R_1lerleR_2`
and `B=(mu_0)/(2pi) i/r for rgeR_2`