Find the magntiude and diraction of the magnitude induction vector `B`
(a) of an infinite palne carrying a current of linear density I, the vector `i` is the same at all points of the plane,
(b) of two parallel infinite planes carrying currents of linear densities a dn -1, the vectors `i` and `-i` are cohnstant at all points of the corresponding planes.

Explanation

(a) We apply circulation theorem as shwon. The current is vertically upwards in the plane and the magnitude field is horizontal and parallel to the plane.
`oint vec(B). d vec(l) = 2 Bl = mu_(0) il` or, `B = (mu_(0) i)/(2)`
(b) Each plater contributes `mu_(0) (i)/(2)` between the planes that cancel.
Thus
`B={{:(mu_(0)i" between the plane"),("0 outside."):}`