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

Hysteresis Loop

Some Magnetic properties

Outline:

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.

Comparing two Hysteresis loops

Another example of hysteresis loop is shown below:

Hysteresis Loop

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