Magnetism and Matter 2 Flashcards
what is magnetisation(I)/ intensity of magnetisation
Magnetization, also termed magnetic polarization, represents the extent to which a material is magnetised when placed in a magnetising field.
It is the net dipole moment induced in a material per unit volume.
I is a vector with dimensions L–1 A and is measured in a units of A m–1
.
What is magnetising force/ Magnetic intensity?
It is the magnetic field present in free space and induces magnetism.
consider a toroidal solenoid carrying a current I with the no of turns per unit length l. The magnetic field inside the toroidal solenoid is
B=μ∘nI
for other medium
B=μnI
The quantity nI is called magnetising force or magnetic intensity.
SI unit: Am-1
WHat is magnetic flux
No of magnetic field lines passing normally through a surface
Unit: Tm^2 or Weber (Wb)
Magnetic flux density
defined as the magnetic field lines passing per unit volume normal ot the surface
ɸ/A=B
Unit:T or Wbm-2
Magnetic susceptibility
Its gives the measure of ability of substance to take up magnetisation when placed in a magnetic field.
ratio of intensity of magnetisation o the magnetic field intensity.
χ is small and positive for materials, which are called
paramagnetic. It is small and negative for materials, which are termed
diamagnetic.
χ=I/H
Magnetic permeability
It is the ability of a material to allow the passage of magnetic field lines through it. It is a measure of the conducting propwerty of the material to magnetic field lines.
it is the ratio of the magnetic flux density to magnetic intensity.
u=B/H
Unit:TmA-1
relative permeability
analogous to dielectric constant,
Ratio of permeability of freespace/vaccum to the the given medium.
what are diamagnetic substance
Diamagnetic substances are those which have tendency to move from
stronger to the weaker part of the external magnetic field.
They develop feeble magnetism in the direction opposite to that of applied field.
what is the cause of diamagnetism
Electrons in
an atom orbiting around nucleus possess orbital angular momentum.
These orbiting electrons are equivalent to current-carrying loop and thus
possess orbital magnetic moment. Diamagnetic substances are the ones
in which resultant magnetic moment in an atom is zero. When magnetic
field is applied, those electrons having orbital magnetic moment in the
same direction slow down and those in the opposite direction speed up.
This happens due to induced current in accordance with Lenz’s law which
you will study in Chapter 6. Thus, the substance develops a net magnetic
moment in direction opposite to that of the applied field and hence repulsion
In a diamagnet material, there are paired electrons whcih are moving in the opposite direction so the net magnetic moment i 0.
When an externalmagnetic field is applied one electron is accelerated and other is decelerated. Therefore the net magnetic moment increases and indiuced in the opposite direction.
examples of diamagnetic materials
Some diamagnetic materials are bismuth, copper, lead, silicon,
nitrogen (at STP), water and sodium chloride, Hg at room temp
what happens when a diamagnetic material is kept in an external field
The field lines are repelled or expelled and the field inside
the material is reduced. In most cases, this reduction is slight, being one
part in 105
. When placed in a non-uniform magnetic field, the bar will tend
to move from high to low field.
what is meissner effect
These
are metals, cooled to very low temperatures which exhibits both perfect
conductivity and perfect diamagnetism. Here the field lines are completely
expelled! χ = –1 and µr
= 0. A superconductor repels a magnet and (by
Newton’s third law) is repelled by the magnet. The phenomenon of perfect
diamagnetism in superconductors is called the Meissner effect, after the
name of its discoverer. Superconducting magnets can be gainfully
exploited in variety of situations, for example, for running magnetically
levitated superfast trains.
what happens to susceptibility of diamagnetic materials with temp
it is indepenent of temperature or magnetising field,
