So, electricity and magnetism are closely
linked.
We already saw that using electric current
we can produce an electromagnet.
Another example of the connection is that
if we have an electric charge, say an electron,
that is moving near a magnet there’s a force
that acts on that moving charge and that will
deflect the path of action.
Here's an example of this.
[Buzzing] I'm going to produce an ele- an
electron beam in this Crooke’s tube.
So, you see that electron beam, and now I’m
going to take this magnet, the big horse shoe
magnet.
And you see how the- the beam gets deflected
in all different directions by the magnet.
There’s a similar effect you can do if you
have an old TV.
These old TVs use electron beams to light
up the screen, and if you bring the big magnet
near the screen.
Now, this can damage the picture of the screen
permanently, so don't do this if you are still
using that television set.
But you see how distorted and warped the image
becomes.
And this is because the electron beams in
the cathode ray tube are being bent and deflected
by the magnet.
Now, the moving charges don’t have to be
moving in a vacuum or in space.
The electric charges that are moving in a
current that’s passing through a wire also
feel that force.
So, we’ll see this.
I’m gonna turn on- See when I turned on
the current, the wire jumps out; see that
again.
So, that Lorentz force acted on the electrons
moving on the wire- sorry- in the wire, and
the magnetic field produced that Lorentz force
on those moving charges and actually pushed
the wire away.
Now, another connection between electricity
and magnetism is electromagnetic induction.
So, I can use this Lorentz force on charges
and if I have a magnet that’s moving towards
a coil, that will actually move the charges
in the coil and will get a current.
So, if I'm, in this case, when I'm moving
the large horse-shoe magnet towards this-
this coil, the charges move in one direction-
I have a current in one direction.
When I move the magnet away, the charges move
in another direction.
If I don't move the magnet, if I just hold
the magnet still, then the current stops.
Let’s see how this works.
You see the magnet sitting there, now when
I start moving it, you see that the meter
is indicating the current.
And the faster I move the magnet, the more
current I can produce.
Now, when I just stop, if I just place the
magnet nearby, the current doesn't- isn't
produced.
But just as soon as I start moving the magnet,
I'm getting nice big current.
Now, instead of physically moving a magnet
back and forth, I can use an alternating current
electromagnet.
Now, when I have an electromagnet with alternating
current, when the current is moving one way,
the North Pole is on one side, and then when
the current moves the other way, the South
Pole is on that side.
So, basically I can create an oscillating
magnetic field using an electromagnet that’s
driven by alternating current.
Now, that alternating oscillating magnetic
field will produce a current in objects.
So, if I put a metal ring near this AC magnet,
I'll notice that it starts getting hot by
Ohmic heating which tells me that there’s
a current in that metal ring.
Now, I can also measure that current just
by having say a coil of wire with a bulb.
So, here I have this coil of wire with a bulb
connecting the ends.
I just turned on the AC electromagnet; you
see that when I put the coil near the magnet,
it induces a current in that coil.
Okay.
So, that coil is just a big loop of wire with
the two ends connected to the light bulb,
and this AC electromagnet is inducing a current
in that coil.
Now, a more dramatic example of creating current
using a fluctuating magnetic field is the
so-called EMP or electromagnetic pulse.
So, if you have say a nuclear bomb and that's
in the atmosphere, there’s kind of a complicated
process, but this can produce an intense rapidly
fluctuating magnetic pulse.
And the current that’s induced by this EM
pulse, can be so large that it can actually
knockout circuits, possibly by Ohmic heating
if the current is really a large amperage.
And this happened in 1962 during a nuclear
test.
Even though the explosion was 900 miles away
from Hawaii, it actually knocked out 300 streetlights
and TV- sorry- telephone service.
Now, this EMP is a very popular plot device
and here you see just a handful of films that
use it, there's many more.
Now, one thing that happens is when this oscillating
magnetic field induces a current, in say a
coil, that current -we know that whenever
we have a current moving in a coil, that produces
an electromagnet.
So, this oscillating magnetic field creates
a current.
That current produces an electromagnet, and
this effect is called self-induction.
Now, that secondary magnetic field that's
due to the induced current, it is always in
the opposite direction from the primary magnetic
field that produces it.
So, if I have say an AC magnet with a ring
that I put near the top of the magnet, that
secondary magnetic field will always be opposing
or in the opposite direction from the magnetic
field created by the AC electromagnet.
I know that’s kind of complicated, but let’s
look at a little demonstration of this because
it’s kind of an interesting effect.
[Metalic clinking] I put that ring of metal.
And now I turned on the magnet and you see
that there is now a repulsion between the
AC electromagnet and this ordinary ring of
metal.
So, as I said, the ring of metal- there’s
a current that goes through it.
If you touch that ring, you’ll see that
it actually got hot and that current produces
the secondary magnetic field, that cause of
levitation.
One way to sort of realize that there's a
current and that it's necessary is that if
I take a similar ring but with a slice taken
out of it, so it has a cut.
So, there’s a second ring but it has a cut.
I turn on the AC electromagnet and nothing
happens because I can't get a current flowing
around it because there's a gap in the ring.
There’s this AC electromagnet because the
magnetic field is fluctuating.
It’s not as powerful as a standard electromagnet.
Another effect that occurs is if I drop a
strong magnet in a copper pipe that secondary
magnetic field, well it's in the case of the
ring it was levitating this doesn't levitate
the magnet, but it does cause it to fall extremely
slowly.
It can't stop it because once it stops it,
we no longer induce a current and we no longer
have that secondary field.
So watch when we drop this magnet, here it
goes.
Notice how slowly it’s falling and finally
reaches the bottom.
Now copper is not ferromagnetic.
You have it tilted, that’s the only problem.
I know, well let me get it here.
You tilt this as if we are holding it straight.
Yeah.
Is that good?
So watch how it falls.
So it's not sticking to the sides because
copper is not ferromagnetic, but that induced
current creates that force that makes it fall
very slowly.
Now, finally the most interesting connection
between electricity and magnetism is that
when we have oscillating electric and magnetic
fields this actually propagates as a wave
is called electromagnet magnetic waves.
And examples of electromagnetic waves are
radio waves, microwaves, infrared, ultraviolet
and most important to us visible light.
So these are transverse waves created by oscillating
electric and magnetic fields.
So, in the summary….
So 
we saw that in the magnetic levitation and
in the magnetic breaking, which was the magnet
falling very slowly down a metal pipe.
And then finally…
An important example that is visible.
So, that is a summary of the connections between
electricity and magnetism finishing with appropriately
enough light.
