Page 486 - Basic Electrical Engineering

Substituting values

Field intensity at P at a perpendicular distance of from the coil of radius r
is

Substituting value

or,

5.3 MAGNETIZATION CURVE OF A MAGNETIC MATERIAL
Electromagnets are produced by winding a coil around a piece of magnetic

material, say iron, and passing current through the coil. When current is
increased gradually, the flux will increase. The rate of increase of the flux

produced with increase in current will slow down after a sufficient increase of
current as shown in Fig. 5.11. The core is said to be saturated when further

increase of current through the coil does not cause further increase of flux.
The flux per unit area is expressed as flux density B.