Page 501 - Basic Electrical Engineering

In Fig. 5.20 is shown an electromagnet having N number of turns and the
coil carrying a current, I. The cross-sectional area of the core is A. An iron
piece is separated from the electromagnet by a distance, l. We will calculate

the energy stored in the magnetic field and the lifting power of the
electromagnet.

Energy stored in a magnetic field is given by

Putting

Again

Therefore,

Again,

B = μ H,
°

or,

Considering the magnetic field in the air gap between the magnet and the
piece of iron,

Energy stored,