1-1
Section 1
Introduction
UNDERSTANDING FLUX DENSITY
Magnetic fields surrounding permanent magnets or electrical conductors can be visualized as a collection of
magnetic
flux
lines; lines of force existing in the material that is being subjected to a magnetizing influence.
Unlike light, which travels away from its source indefinitely, magnetic flux lines must eventually return to the
source. Thus all magnetic sources are said to have two
poles
. Flux lines are said to emanate from the “north”
pole and return to the “south” pole, as depicted in Figure 1-1.
Figure 1-1
Flux Lines of a Permanent Magnet
One line of flux in the CGS measurement system is called a
maxwell
(M)
,
but the
weber
(W), which is 10
8
lines, is more commonly used.
Flux density, also called magnetic induction, is the number of flux lines passing through a given area. It is
commonly assigned the symbol “
B
” in scientific documents. In the CGS system a
gauss
(G) is one line of flux
passing through a 1 cm
2
area.
The more commonly used term is the
tesla
(T)
,
which is 10,000 lines per cm
2
. Thus
1 tesla = 10,000 gauss
1 gauss = 0.0001 tesla
Magnetic field strength is a measure of force produced by an electric current or a permanent magnet. It is the
ability to induce a magnetic field “
B
”. It is commonly assigned the symbol “
H
” in scientific documents. The unit
of “
H
” in the CGS system is an
oersted
(Oe), but the
ampere-meter
(Am) is more commonly used. The
relationship is
1 oersted = 79.6 ampere-meter
1 ampere-meter = 0.01256 oersted
It is important to know that magnetic field strength and magnetic flux density are not the same. Magnetic field
strength deals with the physical characteristics of magnetic materials whereas flux density does not. The only
time the two are considered equal is in free space (air). Only in free space is the following relationship true:
1 G = 1 Oe = 0.0001 T = 79.6 Am
