Important Questions of Magnetic Hysteresis
In this post, some of the important questions of magnetic hysteresis are given. It includes meaning of magnetic hysteresis, residual flux density, coercive force, significance of hysteresis loop, shape of hysteresis loop, magnetic memory material, hysteresis loss, screening effect, how to reduce hysteresis loss, Steinmetz hysteresis coefficient, BH Curve of magnetic material, eddy current loss, how to reduce eddy current loss, applications of eddy current loss, force on current carrying conductor and Fleming’s left-hand rule.
What do you mean by the magnetic hysteresis?
Magnetic
hysteresis
The hysteresis means to lag behind. When a magnetic
material is magnetized in the magnetic field, there is always some magnetism
after removing magnetizing force. Therefore the flux density (B) in the
magnetic material always lags behind the magnetizing force (H). This phenomenon
is known as magnetic hysteresis.
What do you mean by the residual flux density?
Residual
flux density
Once the magnetic core is magnetized and if the
magnetizing force is removed, the core is not completely demagnetized but the
flux density has still some value. It is called as residual magnetism.
Explain the term: Coercive force
Coercive
force
The demagnetizing field strength required to wipe off
residual magnetism in the magnetic material is called as coercive force.
What is area of hysteresis loop indicating?
The area of the hysteresis loop indicates the energy
absorbed by the core material to overcome friction involved in changing the
alignment of magnetic domains for complete cycle.
Describe the significance of rectangular shape of hysteresis loop.
Significance
of the shape of hysteresis loop
The rectangular shape of the hysteresis loop suggests
that the flux density remains constant at the maximum value until magnetic
field strength is changed to its negative maximum value. The ferrite material
has rectangular type hysteresis characteristics.
Which material is used for magnetic memory in the computers? Why?
The ferrite is used for magnetic memory in the
computers.
Why hysteresis loss occurs in the magnetic material?
Hysteresis loss
When the magnetic material is magnetized, its domains
are aligned in the direction of the applied field. If the magnetic material is
magnetized in the reverse direction its domains try to align into reverse
direction. The domains rotate in both directions after complete cycle of
magnetic field in this way.
There is a loss in this process called as hysteresis
loss.
How hysteresis loss can be reduced?
The hysteresis loss can be reducing by using materials
which have low hysteresis co – efficient.
Which are the parameters affecting the hysteresis losses?
The hysteresis loss per meter3 per cycle of
magnetic material depends upon (a) The maximum flux density established in the
material.( b ) Quality or type of magnetic material.
What is Steinmetz hysteresis co – efficient?
Steinmetz
hysteresis co – efficient
The hysteresis loss Wh α Bmax joule/meter3/cycle
Wh = η Bmax joule / meter3 / cycle ( Where η
= Steinmetz hysteresis co – efficient in joule / meter3 / cycle and
its value depends upon the type of magnetic material )
Whether the B – H curve of magnetic material is linear? Why?
B
– H curve
The relative permeability of
magnetic material is not constant but depends upon the flux density therefore
the B – H curve is not linear.
B = μH
B = μ0 μrH
μr = ( B / μ0H
)
Whether the B – H curve of non – magnetic material is linear? Why?
The relative permeability of
non – magnetic material is constant therefore the B – H curve of the non –
magnetic material is linear.
Explain: Eddy current loss
Eddy
current loss
The core material is made of concentric shells. As the
iron is conducting material, each shell may be treated as a closed coil.
Therefore, an emf is induced in each shell due to flux
links with the each shell. This emf causes a large current flow due to small
resistance of the core. This current causes losses in the core which is better
known as eddy current loss.
How eddy current loss can be minimized?
Eddy current loss
The eddy current loss can be minimized by using core
of laminations having thickness varies from 0.45 to 0.5 mm in the electrical
machines. Each lamination is insulated from each other by using thin coating of
oxide or varnish.
What is the direction of eddy current in the core material?
The direction of the eddy current is always
perpendicular to the direction of the magnetic flux.
Why the value of eddy current loss is very large in the solid core material?
The cross section of the solid core material is very
large. Therefore, its resistance is very small and thus large eddy current flow
in the solid core material.
State the typical applications of eddy current.
Applications of eddy current
Induction heating
Damping torque in the PMMC instruments
Electrical braking in induction instruments
What do you mean by the screening effect?
Screening effect
The flux density at the centre of the core is lower
than the outer surface due to flow of eddy current in the core. It is known as
screening effect.
State the Fleming’s left-hand rule
Fleming’s left-hand rule
Keep first finger, middle finger and thumb such that
they are mutually perpendicular. If the first finger shows the direction of the
magnetic field, middle finger shows the direction of the current, the thumb
indicates the direction of the force.
On which parameter the force of attraction or repulsion depends when two current carrying conductors are placed in parallel?
Force
on parallel current carrying conductors
Force of attraction: If the direction of the currents
in both conductors is in the same direction.
Force of repulsion: If the direction of the currents
in both conductors is in the reverse direction.
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