Class 12 Exam > Class 12 Videos > L23 : Electron theory of dimagnetism - Matter & Magnetism, Physics, Class 12
L23 : Electron theory of dimagnetism - Matter & Magnetism, Physics, Class 12 Video Lecture
FAQs on L23 : Electron theory of dimagnetism - Matter & Magnetism, Physics, Class 12 Video Lecture
| 1. What is the electron theory of diamagnetism? |  |
Ans. The electron theory of diamagnetism states that when a material is placed in an external magnetic field, the orbital motion of its electrons causes the material to develop a magnetic field of its own. This induced magnetic field opposes the applied magnetic field, resulting in the material being repelled by the magnet.
| 2. How does the electron theory of diamagnetism explain the behavior of diamagnetic materials? | |
Ans. According to the electron theory of diamagnetism, diamagnetic materials have all their electron orbits completely filled. When these materials are exposed to an external magnetic field, the electrons in their orbits experience a force that opposes the applied field. This leads to the development of an induced magnetic field in the opposite direction, causing the material to repel the magnet.
| 3. Can you provide an example of a diamagnetic material? | |
Ans. One example of a diamagnetic material is bismuth. Bismuth is a lustrous, brittle, and pinkish-white metal that exhibits strong diamagnetic properties. When a bismuth sample is placed near a magnet, it will be repelled and move away from the magnet.
| 4. How does the electron theory of diamagnetism differ from the electron theory of paramagnetism? | |
Ans. The electron theory of diamagnetism and paramagnetism differ in terms of the electron behavior in response to an external magnetic field. In diamagnetic materials, all the electron orbits are completely filled, and the induced magnetic field opposes the applied field. On the other hand, in paramagnetic materials, there are unpaired electrons that align their spins with the applied field, resulting in a net magnetization in the same direction as the field.
| 5. Are all materials diamagnetic or paramagnetic? | |
Ans. No, not all materials are diamagnetic or paramagnetic. Some materials, known as ferromagnetic materials, exhibit a much stronger response to an external magnetic field compared to diamagnetic or paramagnetic materials. Ferromagnetic materials can be permanently magnetized and retain their magnetization even after the external magnetic field is removed. Examples of ferromagnetic materials include iron, nickel, and cobalt.
Text Transcript from Video
hello friends this video on matter and
magnetism part 23 is brought to you by
example.com no more fear from exam
please make sure that you have watched
all the videos to the part 22 before
going ahead with part 23 now let us look
at the concept of diamagnetism from
electron theories point of view so we
will now see the behavior the
diamagnetic materials behavior which I
listed in the previous slides why does
that occur so now we already know that
for any electron there are two magnetic
moments associated with it the first one
is the orbital magnetic moment which is
because of the orbital motion of the
electron by virtue of this orbital
motion of the electron around the
nucleus it has a magnetic moment that is
orbital magnetic moment which we
generally denote as mu M right also
there is another magnetic moment
associated with every electron by virtue
of its spin so mu L and mu s these are
the two or by magnetic moments
associated with any electron so we can
say that the net magnetic moment for any
electron is basically given by the
orbital magnetic moment plus the spin
magnetic moment so the vector sum of
these two magnetic moments will give you
the net magnetic moment for any electron
so when we talk about the diamagnetic
substance what happens is that in a
diamagnetic substance this image and M s
that is the orbital magnetic moment and
spin magnetic moment cancel each other
for every atom so as a result the atom
has no net magnetic moment so what
happens for a diamagnetic substance the
orbital magnetic moment and the spin
magnetic moment they cancel out
therefore the atom has no net magnetic
moment the
is the net magnetic moment becomes zero
for every atom okay so what we can see
that so that is why in a diamagnetic
substance we say that every atom has
each atom has zero net dipole moment
they do not have a net dipole moment so
what we can consider they occur in this
scenario we can consider that electron
inside an atom is easy equivalent to two
electrons moving with same angular
velocity but in opposite sense that
means I mean what did we completely
conclude that in a diamagnetic substance
for each atom the net magnetic moment is
equal to zero so now when we consider
one atom we can say that one atom has
two electrons which are moving with same
angular velocity but in opposite
direction so if there are two electrons
moving with same velocity but in
opposite direction then the net magnetic
moment will be zero right
so let us assume that kind of scenario
so we can assume that electrons inside
atom can be considered as equivalent to
two electrons moving with same velocity
in opposite sense right some good like
this let us suppose this is the nucleus
and this is the electron so let us
suppose in one case the electron is
moving in this direction and the other
electron is moving in this direction
right so we can assume that each atom
consists of two electrons both are
moving with same angular velocity but in
opposite direction
so in this case what would be the
magnetic force experienced by this
electron now if the electron is moving
in this direction that means what is the
direction of current flow electron is a
negatively charged particle right so
that means the current flow is in the
opposite direction so this mode
the direction of current flow now how do
you guys how do you determine the
direction of force force will be given
by Q into V cross B right let us know
now right now there is no magnetic field
right so right now I am just imagining
that in this case these two electrons
moving with same angular velocity but in
opposite sense so magnetic net magnetic
moment in this case is equal to zero so
this is the scenario as long as we have
not applied any magnetic field now what
will happen when I apply an external
magnetic field actually you forget about
this force part right now because right
now I am NOT talking about magnetic
field at all I just talked about when no
magnetic field is applied what happens
in a diamagnetic substance in a
diamagnetic substance the orbital
magnetic moment and the spin magnetic
moment of each atom cancel out therefore
the net magnetic moment of each atom is
equal to zero therefore we can assume
that inside each atom there are two
electrons which are moving with same
angular velocity but in opposite sense
so we conclude that in absence of
magnetic field net magnetic moment of
each atom is zero now we will look at
the scenario when we apply some magnetic
field what what happens when we apply an
external magnetic field in that case the
scenario would be something like this so
what did we assume till now we said that
let us suppose this is the electron this
is the first electron and this is the
second electron right we have assumed
that each atom consists of two electrons
moving with same velocity in opposite
sense right so in the first case the
electron is moving in this direction
that means the direction of current flow
is this one so the current is flowing in
this direction similarly here also the
direction of current flow is this
direction now when a magnetic field is
applied we assume
a magnetic field is applied in the
downward direction let us suppose we
have assumed them we have applied a
magnetic field in the downward direction
so what would be that now due to this
magnetic field the moving charge will
experience a force right so it will
experience a magnetic force so that
magnetic force is given by Q into V
cross B right so what would be the
direction of the magnetic force you
apply the right-hand rule so by applying
the right-hand rule we can say that in
this case this is the direction of
magnetic field right and what is the
direction of the force acting on this so
the force that will act on the electron
let us suppose at any instant of time
the electron is here so the current
flowing you curl your fingers in the
direction of current right and then it
goes down the electrons are moving in
this direction so here if you if you
consider any point for example this
point here if you see all your fingers
will come towards this direction
direction of current then it will get
folded in the downward direction right
so your thumb will point in this
direction so that means the direction of
the magnetic force experienced by the
electron would be somewhat like this
similarly here in this case when the
electron then the current is going in
this direction in that case your fingers
will fold in that direction at any point
say let us consider this point so the
direction of force by right-hand rule
would come out to be somewhat like this
so what do we observe you observe that
the direction of force in this case is
outward radially outward whereas in this
case the direction of horses towards the
center now what was the direction of
magnetic moment the direction of
magnetic moment in this case since the
electron was moving in this direction so
the current flow was in this direction
so this direction is the current flow so
magnetic moment was acting in this
direction and in this direction in this
case the magnetic moment
was acting in the opposite direction
right now because of this force how will
this affect the magnetic moment now what
do we see in the first case now we talk
about the in presence of magnetic field
in presence of magnetic field this is my
first electron and this is my second
electron so what is happening for the
first electron the magnetic force acts
in the outward direction like that means
it is acting in the outward Direction
means it is acting opposite to the
direction of centripetal force so that
means it is reducing the centripetal
force so because of this F the
centripetal force decreases so it is
decreasing the centripetal force
now if the centripetal force is getting
decreased that means the velocity is
also getting decreased right so velocity
is getting decreased and as a result the
magnetic moment is also getting
decreased now when the magnetic moment
is getting decreased let us suppose that
the magnetic moment get decreased by
some small value Delta M so now the new
magnetic moment becomes earlier it was M
so now it becomes M minus Delta M right
so let me say so let me say now this
magnetic moment becomes M minus Delta M
now what happens in the second scenario
in the second scenario this F acts this
F acts inwards like that means it and
acts in the direction of centripetal
force so that means the centripetal
force increases because of this inward
force F as a result the velocity also
increases and as a result of this
magnetic moment also increases by some
small value Delta M so in this case this
M increases by a small value there
and so now these two electrons are not
two different scenarios they had I mean
they are part of one atom because we
have assumed that one atom is made up of
two electrons while moving in one
direction the other moving in the
opposite direction so what is happening
to the entire atom as a result vector
addition of that what happens to the net
magnetic moment of the atom as a result
the net magnetic moment of atom what
happens the net magnetic moment is
changed by 2 into Delta M by vector
addition length because this magnetic
moment is a vector quantity so so when
you vectorially and these 2 magnetic
moments you see an induced magnetic
moment of to Delta M type so this is
known as induced dipole moment so what
did we observe the main observation was
that by application of an external
magnetic field the net magnetic moment
of the atom increased by 2 Delta M so
earlier what was the net magnetic moment
of the atom when there was no magnetic
field it was 0 but now an a non zero
magnetic moment is induced due to the
application of magnetic field right so
that means in presence of magnetic field
induced magnetic moment of each atom is
2 into Delta M right so now magnetic
moment induced means the atom got
magnetized right so that means a
diamagnetic substance now you understand
the behavior which we studied there
there we studied that in a by
diamagnetic substance the net magnetic
moment is 0 as long as we do not apply
any external field so why is that so now
you understood because the orbital
magnetic moment and the spin magnetic
moment of each atom cancel out as a
result the net magnetic moment is 0 when
magnetic field is applied in that case
some magnetic moment is induced right
but in the direction opposite to the
direction of magnetic field so now
you can see that the direction thing
also you see here the magnetic moment is
M minus Delta M and what is the magnetic
moment here it is M plus Delta M so how
did we get this to Delta M it is nothing
but with which magnetic moment is bigger
M plus Delta M is bigger than M minus
Delta M right therefore vectorial
addition will give M plus Delta M minus
M minus Delta M so what will you get you
will get it as to Delta M so from here
you get this to Delta M like this this
is about magnitude and what about the
direction in case of direction out of
these two whichever is greater that will
dominate so which is greater M plus
Delta M is greater that means the
direction will be along M plus Delta M
now the direction of del M plus Delta M
is opposite to the direction of the
applied magnetic field so that is what
we studied there while we were
discussing the behavior of diamagnetic
materials that when an external field is
applied then a magnetic moment is
induced in the atom there is a net
magnetic moment that is induced and it
is induced in a direction opposite to
the direction of the magnetic field so
this clearly explained that how a net
magnetic moment is induced and how it is
induced in a direction opposite to the
applied magnetic field right so I hope
that it is clear to you now the electron
theory of diamagnetism thank you please
visit exam vo comm to watch free
educational videos try3 online tests get
the best quality study materials study
from the best tutors and mentors and
much more thank you once again
magnetism part 23 is brought to you by
example.com no more fear from exam
please make sure that you have watched
all the videos to the part 22 before
going ahead with part 23 now let us look
at the concept of diamagnetism from
electron theories point of view so we
will now see the behavior the
diamagnetic materials behavior which I
listed in the previous slides why does
that occur so now we already know that
for any electron there are two magnetic
moments associated with it the first one
is the orbital magnetic moment which is
because of the orbital motion of the
electron by virtue of this orbital
motion of the electron around the
nucleus it has a magnetic moment that is
orbital magnetic moment which we
generally denote as mu M right also
there is another magnetic moment
associated with every electron by virtue
of its spin so mu L and mu s these are
the two or by magnetic moments
associated with any electron so we can
say that the net magnetic moment for any
electron is basically given by the
orbital magnetic moment plus the spin
magnetic moment so the vector sum of
these two magnetic moments will give you
the net magnetic moment for any electron
so when we talk about the diamagnetic
substance what happens is that in a
diamagnetic substance this image and M s
that is the orbital magnetic moment and
spin magnetic moment cancel each other
for every atom so as a result the atom
has no net magnetic moment so what
happens for a diamagnetic substance the
orbital magnetic moment and the spin
magnetic moment they cancel out
therefore the atom has no net magnetic
moment the
is the net magnetic moment becomes zero
for every atom okay so what we can see
that so that is why in a diamagnetic
substance we say that every atom has
each atom has zero net dipole moment
they do not have a net dipole moment so
what we can consider they occur in this
scenario we can consider that electron
inside an atom is easy equivalent to two
electrons moving with same angular
velocity but in opposite sense that
means I mean what did we completely
conclude that in a diamagnetic substance
for each atom the net magnetic moment is
equal to zero so now when we consider
one atom we can say that one atom has
two electrons which are moving with same
angular velocity but in opposite
direction so if there are two electrons
moving with same velocity but in
opposite direction then the net magnetic
moment will be zero right
so let us assume that kind of scenario
so we can assume that electrons inside
atom can be considered as equivalent to
two electrons moving with same velocity
in opposite sense right some good like
this let us suppose this is the nucleus
and this is the electron so let us
suppose in one case the electron is
moving in this direction and the other
electron is moving in this direction
right so we can assume that each atom
consists of two electrons both are
moving with same angular velocity but in
opposite direction
so in this case what would be the
magnetic force experienced by this
electron now if the electron is moving
in this direction that means what is the
direction of current flow electron is a
negatively charged particle right so
that means the current flow is in the
opposite direction so this mode
the direction of current flow now how do
you guys how do you determine the
direction of force force will be given
by Q into V cross B right let us know
now right now there is no magnetic field
right so right now I am just imagining
that in this case these two electrons
moving with same angular velocity but in
opposite sense so magnetic net magnetic
moment in this case is equal to zero so
this is the scenario as long as we have
not applied any magnetic field now what
will happen when I apply an external
magnetic field actually you forget about
this force part right now because right
now I am NOT talking about magnetic
field at all I just talked about when no
magnetic field is applied what happens
in a diamagnetic substance in a
diamagnetic substance the orbital
magnetic moment and the spin magnetic
moment of each atom cancel out therefore
the net magnetic moment of each atom is
equal to zero therefore we can assume
that inside each atom there are two
electrons which are moving with same
angular velocity but in opposite sense
so we conclude that in absence of
magnetic field net magnetic moment of
each atom is zero now we will look at
the scenario when we apply some magnetic
field what what happens when we apply an
external magnetic field in that case the
scenario would be something like this so
what did we assume till now we said that
let us suppose this is the electron this
is the first electron and this is the
second electron right we have assumed
that each atom consists of two electrons
moving with same velocity in opposite
sense right so in the first case the
electron is moving in this direction
that means the direction of current flow
is this one so the current is flowing in
this direction similarly here also the
direction of current flow is this
direction now when a magnetic field is
applied we assume
a magnetic field is applied in the
downward direction let us suppose we
have assumed them we have applied a
magnetic field in the downward direction
so what would be that now due to this
magnetic field the moving charge will
experience a force right so it will
experience a magnetic force so that
magnetic force is given by Q into V
cross B right so what would be the
direction of the magnetic force you
apply the right-hand rule so by applying
the right-hand rule we can say that in
this case this is the direction of
magnetic field right and what is the
direction of the force acting on this so
the force that will act on the electron
let us suppose at any instant of time
the electron is here so the current
flowing you curl your fingers in the
direction of current right and then it
goes down the electrons are moving in
this direction so here if you if you
consider any point for example this
point here if you see all your fingers
will come towards this direction
direction of current then it will get
folded in the downward direction right
so your thumb will point in this
direction so that means the direction of
the magnetic force experienced by the
electron would be somewhat like this
similarly here in this case when the
electron then the current is going in
this direction in that case your fingers
will fold in that direction at any point
say let us consider this point so the
direction of force by right-hand rule
would come out to be somewhat like this
so what do we observe you observe that
the direction of force in this case is
outward radially outward whereas in this
case the direction of horses towards the
center now what was the direction of
magnetic moment the direction of
magnetic moment in this case since the
electron was moving in this direction so
the current flow was in this direction
so this direction is the current flow so
magnetic moment was acting in this
direction and in this direction in this
case the magnetic moment
was acting in the opposite direction
right now because of this force how will
this affect the magnetic moment now what
do we see in the first case now we talk
about the in presence of magnetic field
in presence of magnetic field this is my
first electron and this is my second
electron so what is happening for the
first electron the magnetic force acts
in the outward direction like that means
it is acting in the outward Direction
means it is acting opposite to the
direction of centripetal force so that
means it is reducing the centripetal
force so because of this F the
centripetal force decreases so it is
decreasing the centripetal force
now if the centripetal force is getting
decreased that means the velocity is
also getting decreased right so velocity
is getting decreased and as a result the
magnetic moment is also getting
decreased now when the magnetic moment
is getting decreased let us suppose that
the magnetic moment get decreased by
some small value Delta M so now the new
magnetic moment becomes earlier it was M
so now it becomes M minus Delta M right
so let me say so let me say now this
magnetic moment becomes M minus Delta M
now what happens in the second scenario
in the second scenario this F acts this
F acts inwards like that means it and
acts in the direction of centripetal
force so that means the centripetal
force increases because of this inward
force F as a result the velocity also
increases and as a result of this
magnetic moment also increases by some
small value Delta M so in this case this
M increases by a small value there
and so now these two electrons are not
two different scenarios they had I mean
they are part of one atom because we
have assumed that one atom is made up of
two electrons while moving in one
direction the other moving in the
opposite direction so what is happening
to the entire atom as a result vector
addition of that what happens to the net
magnetic moment of the atom as a result
the net magnetic moment of atom what
happens the net magnetic moment is
changed by 2 into Delta M by vector
addition length because this magnetic
moment is a vector quantity so so when
you vectorially and these 2 magnetic
moments you see an induced magnetic
moment of to Delta M type so this is
known as induced dipole moment so what
did we observe the main observation was
that by application of an external
magnetic field the net magnetic moment
of the atom increased by 2 Delta M so
earlier what was the net magnetic moment
of the atom when there was no magnetic
field it was 0 but now an a non zero
magnetic moment is induced due to the
application of magnetic field right so
that means in presence of magnetic field
induced magnetic moment of each atom is
2 into Delta M right so now magnetic
moment induced means the atom got
magnetized right so that means a
diamagnetic substance now you understand
the behavior which we studied there
there we studied that in a by
diamagnetic substance the net magnetic
moment is 0 as long as we do not apply
any external field so why is that so now
you understood because the orbital
magnetic moment and the spin magnetic
moment of each atom cancel out as a
result the net magnetic moment is 0 when
magnetic field is applied in that case
some magnetic moment is induced right
but in the direction opposite to the
direction of magnetic field so now
you can see that the direction thing
also you see here the magnetic moment is
M minus Delta M and what is the magnetic
moment here it is M plus Delta M so how
did we get this to Delta M it is nothing
but with which magnetic moment is bigger
M plus Delta M is bigger than M minus
Delta M right therefore vectorial
addition will give M plus Delta M minus
M minus Delta M so what will you get you
will get it as to Delta M so from here
you get this to Delta M like this this
is about magnitude and what about the
direction in case of direction out of
these two whichever is greater that will
dominate so which is greater M plus
Delta M is greater that means the
direction will be along M plus Delta M
now the direction of del M plus Delta M
is opposite to the direction of the
applied magnetic field so that is what
we studied there while we were
discussing the behavior of diamagnetic
materials that when an external field is
applied then a magnetic moment is
induced in the atom there is a net
magnetic moment that is induced and it
is induced in a direction opposite to
the direction of the magnetic field so
this clearly explained that how a net
magnetic moment is induced and how it is
induced in a direction opposite to the
applied magnetic field right so I hope
that it is clear to you now the electron
theory of diamagnetism thank you please
visit exam vo comm to watch free
educational videos try3 online tests get
the best quality study materials study
from the best tutors and mentors and
much more thank you once again
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