Magnetism
 also called lines of force
APPLICATIONS OF MAGNET
MAGNETIC FLUX
Motors, generators,  telephones,  relays, 
loudspeakers,  computer hard drives and
floppy disks,  anti-lock brakes,  cameras, 
fishing reels,  electronic ignition systems, 
keyboards,  t.v.  radio components, 
Transmission equipment.
 the amount of magnetic field (or number of
lines of force) produced by the magnetic source
WHAT IS A MAGNET?
A magnet is a material or object that produces a
magnetic field.
A permanent magnet is a piece of ferromagnetic
material (such as iron, nickel or cobalt) which
has properties of attracting other pieces of these
materials.
It has two poles, North and South
MAGNETIC FIELD
 area around the magnet
 symbol is phi (ф)
 Unit is weber (Wb)
NOTE: 1 x 10^8 lines of force or magnetic field
lines = 1 Weber
MAGNETIC FLUX DENSITY
 the amount of flux passing through a defined
area that is perpendicular to the direction of the
flux.
 Symbol is B
 Unit is Tesla (T)
 Formula B = ф / A
 NOTE: 1 Tesla = 1Weber/m^2
 a force that exists around the magnet
SAMPLE PROBLEMS
1. If a magnetic flux has 3000 lines, find the
number of microwebers.
B = ф/a = 0.00015wB/0.02M^2 = 7.5mT = 0.0075T
= 7.5 x 10^-3 T
3 x 10^-3 Weber = 0.003 weber
4. The maximum working flux density of a
lifting electromagnet is 1.8T and the effective
area of a pole face is circular in cross section. If
the total magnetic flux produced is 353 mWb,
determine the radius of the pole faces.
x 10^-6
3000 lines*1wb/100000000lines = 0.00003 weber =
30microweber = 30000 nanoweber = 0.03
mill;iwb
2. What is the flux density in teslas when there
exists a flux of 600 microweber through an area
of 0.0003 sq. m.?
B = ф/A = 0.0006/0.0003 = 2T
3. A magnetic pole face has a rectangular section
having dimensions 200mm by 100mm. If the
total flux emerging from the pole is
150microweber, calculate the flux density.
1cm = 10mm; 100cm = 1 m; 1000mm = 1m
200mm*1m/1000mm = 0.2m
Dimension of rectangular pole face = 0.2m x
0.1m
Area = 0.2x 0.1 = 0.02m^2
Given: B = 1.8T
A = pi(r^2)
B = ф/A;
r=?
ф = 0.353Wb
A = ф/B
A = 0.353Wb/1.8 Wb/m^2 = 0.1961m^2;
Wb*m^2/Wb
0.1961 m^2 = pi(r^2)
r = 0.2498m = 249.8mm = 24.98cm