Diapole analogy of electrostatic vs magnetic - Magnetism & Matter Video Lecture - Class 12

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magnetism part eight is brought to you
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please make sure that you have watched
all the videos to the part 7 before
going ahead with part 8 now when we look
at the dipole analogy of electrostatics
and magnetism because we when we talk
when mr. electrostatics we talk about
electric dipole now that we are studying
magnetism we are talking about magnetic
dipole but there is a great analogy
between the two if you look at them the
formulae or if you look at the
expressions which we have derived to
calculate the magnetic fields at
equatorial point or at an axial point or
the torque experienced by the magnetic
dipole or in an external field or the
energy related to the magnetic dipole in
an external field you will see that the
expressions are completely similar in
both the cases just that you replace few
things here and there for example when I
talk about dipole moment in
electrostatics and magnetism when I when
I am talking about electrostatics dipole
moment means electric dipole moment
which we denote by P when I talk about
dipole moment in magnetic dipole I mean
to say magnetic dipole moment which is M
right in stare you have electric dipole
moment and here you have the magnetic
dipole moment or nothing but the
magnetic moment which we often call as
we generally call it as magnetic moment
instead of magnetic dipole moment like
similarly when I talk about the
equatorial field that means the magnetic
field at an equatorial point for an
electric dipole when I talk about
electric dipole it is somewhat like this
a plus Q a minus Q separated by a
distance to a right so when I talk about
an equatorial field that means the
magnetic field at some equatorial point
P so what what does that magnetic field
which we find it is 1 by 4 pi
silent not be divided by our Chu now
when I talk about the equatorial field
for a magnetic dipole there we find that
it is minus mu naught by 4 PI into M by
r-cube so if you look at both the
expressions it is exactly the same just
that instead of 1 by epsilon naught here
you have mu naught here where it was
permittivity and here it is permeability
and instead of electric dipole moment
you have the magnetic moment similarly
when we talk about axial point here it
was 1 by 4 pie epsilon-not to P divided
by r cube and here it was mu naught by 4
pi 2 m divided by r cube this i have
already derived and showed you how it is
me or not by 4 pi 2 m by r cube if you
want you can derive these expressions as
well following the same way as we do as
you did for electrostatics now what is
was the thought experienced in external
fields in case of electro in a case of
an electric dipole it was nothing but p
cross e that is the magnetic dipole
moment cross product with electric field
and here it was the magnetic moment that
is M cross product external magnetic
field right and energy in external field
here it was minus p dot e and here it
was minus m dot b right so if you see
they resemble each other to a great
extent just that when we talk about
magnetism all the electric field gets
replaced by magnetic field and all the
electric dipole moments get replaced by
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