A system consists of two parallel planes carrying currents producing a unifrom magnetic field of induction `B` between the planes. Outside this space there is no magnetic field. Find the magnetic force acting this space there is no magentic field. Find the magnetic force acting per unit area of each plane.

Explanation

By the circulation theorem `B = mu_(0) i`,
where `i` = current per unit length flowing along the plane perpendicular to the sphere. Currents flow in the opposite sense in the two planes is just `(1)/(2) B`. The force on the plate in,
`(1)/(2) B xx i xx` Length `xx` Breadth `= (B^(2))/(2 mu_(0))` per unit area.
(Recall the formula `F = BIl` on a straight wire.)