Mehran University Of Engineering & Technology
SZAB Campus Khairpur Mir’s
Subject:Theory Of EMF
Hysteresis Loop & Some Magnetic Properties
(Topic)
Presenting Roll No:
K-12 EL 28
Hysteresis
When an external magnetic field is applied to
a ferromagnetic such as iron, the atomic dipoles align
themselves with it.
Even when the field is removed, part of the alignment will be
retained: the material has become magnetized.
This lagging behind of flux density(B) or magnetization to
magnetizing force(H) is called Hysteresis or Hysteresis Loss.
Some compositions of ferromagnetic materials will retain an
imposed magnetization indefinitely and are useful as
"permanent magnets".
A hysteresis loop shows the relationship between the
induced magnetic flux density (B) and the magnetizing
force (H).
It is often referred to as the B-H loop or curve
The loop is generated by measuring the magnetic flux of
a ferromagnetic material while the magnetizing force is
changed.
This property of ferromagnetic materials is useful as a
magnetic "memory".
Hysteresis Loop
B & H
Magnetic flux density (B):
The amount of magnetic flux through a unit area taken
perpendicular to the direction of the magnetic flux.
It is expressed by the force per unit length on a
conductor carrying unit current at a point near it.
Magnetizing Force (H):
It is the force which depends upon the current which is
passed through a magnetic material to magnetize it.
Magnetic Properties
Retentivity :It is a material's ability to retain a certain
amount of residual magnetic field when the magnetizing
force is removed after achieving saturation.
Residual Magnetism or Residual Flux : the magnetic
flux density that remains in a material when the
magnetizing force is zero.
Coercive Force : The amount of reverse magnetic field
which must be applied to a magnetic material to make
the magnetic flux return to zero.
Magnetic Properties
Permeability (m): It is a material property that describes
the ease with which a magnetic flux is established in a
component. It is the ratio of the flux density (B) created
within a material to the magnetizing field (H) and is
represented by the following equation:
m = B/H
Reluctance : It is the opposition that a ferromagnetic
material shows to the establishment of a magnetic field.
Reluctance is analogous to the resistance in an electrical
circuit.
References:
Internet Links:
http://en.wikipedia.org/wiki/Hysteresis#Magnetic_hysteresis
http://magician.ucsd.edu/essentials/webbookse26.html
http://wiki.answers.com/Q/What_is_hysteresis_loss
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/hyst.html
http://www.ndt-ed.org/EducationResources/CommunityColleg
e/MagParticle/Physics/HysteresisLoop.htm
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