
Electromagnetism 167
10.7 Relative and absolute permeabilities
Using a magnetic core, such as steel inserted into a coil, increases
the flux produced by a given
m.m.f.
The ratio of the flux density in a
magnetic material to the flux density in a non-magnetic material
produced by the same magnetic field strength is called the relative
permeability, denoted by the symbol u.
r
. For a magnetic core,
therefore,
B
= ji
0
p.
r
//
The product |x
0
u.
r
is called the absolute permeability, u., and
B = ILH
B
Since u.
r
varies for different values of the magnetic field strength
(H),
it is convenient to represent the relationship between the flux
density (B) an ...