In the core of the electromagnet there is a small gap l, in which a plate of the same material is placed (figure). How much work must be done against magnetic forces to remove the plate from the gap? The perimeter of the core is equal to L, the cross section is the same everywhere and is equal to S, the magnetic permeability is m > 1, the current through N turns of the winding is equal to I. Neglect magnetic field scattering.

Answer. Format gif