A long, cylindrical wire of radius b carries a current i distributed uniformly over its cross section. Find the magnitude of the magnetic field at a point inside the wire at a distance a from the axis.

Explanation

By Ampere's circuital law `intB.dl = mu_oi`
For given conditions B.dA = mu_oi.dx`
`rArr Bint dA = mu_oi int dx`
`rArr B.2pib^2 = mu_oia`
`rArr B = (mu_oia)/(2pib^2).`