chapter  11
14 Pages

Magnetic Materials

A moving charge creates a magnetic field. If this moving charge takes place as current in a wire, the magnetic field flows around the wire. When the wire is formed into a coil the magnetic lines of flux reinforce each other and thereby increase the field within the coil (Figure 11.1a), which is given by

(11.1)

where

H

=

magnetic field strength

N

=

the number of turns within the coil

I

=

current

l

=

coil length

In what used to be the more common centimeter-gram-metric (cgs) units,

H

was expressed in oersteds when

I

was in amperes and

l

was in centimeters. The System International (SI) units for

H

is ampere turns per meter, more often expressed as amperes per meter (A/m).