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- [Instructor] In other
videos, we talk about

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how a current flowing through a wire

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can induce a magnetic field.

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Now what we're going to
talk about in this video

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is how we can go the other way.

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How a change in a magnetic field

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can affect or induce a
current in a loop of wire.

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We're gonna be going from a change,

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change in, and actually we're
gonna focus on magnetic flux.

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Magnetic.

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Magnetic flux through a loop.

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Through a loop.

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Now we're going to see how this actually

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induces a current in that loop.

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So, induces.

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Induces a current.

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Induced current.

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This right over here,

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all right, this is my attempted
drawing a magnetic field

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and these are the magnetic field lines.

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They don't look like lines

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because they're all
popping out of the screen.

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They're moving towards
you, towards the viewer

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so you could view these
as the tips of the arrow.

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Now there's different ways
of showing magnetic fields.

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You could show magnetic
field lines like this,

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you could also use vectors.

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And when you're using field lines,

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it's the density of the field lines

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tell you how strong the magnetic field is.

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If you got to the right here,

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they are less dense and
so the magnetic field

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is less strong on the
right hand side over here

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than they are on the left hand side,

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or at least that's what
I'm trying to depict.

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Now if we did it with vectors

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we would have bigger arrows
pointing out over here

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than we would over here.

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But now let's do a loop of,

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let's do a loop of wire.

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Let me draw a loop of wire here.

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Let's say I have a loop of wire that is,

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this is my loop of wire.

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My loop of wire.

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If I just throw that loop of wire

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and if it's just stationary,
it's in this magnetic field

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and the magnetic field isn't changing,

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I do have some flux going through the,

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I guess you can say the
surface defined by this wire.

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And if you're unfamiliar
with the term magnetic flux,

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I encourage you to watch
the video on magnetic flux.

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But if I just have this wire

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stationary in the magnetic field,

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nothing is going to happen.

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But I will be able to induce a current

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if I change the magnetic flux

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going through this surface in some way.

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So for example, right
now the magnetic field

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is pointing out of the screen.

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If I were to make it even stronger

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in the direction pointing
out of the screen.

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So, I guess one way to think about it is

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if I were to, if the change
in the magnetic field,

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the change in the flux
were to get even stronger

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in the outward direction.

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So I don't know, a good way to,

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just gonna get even stronger
in the outward direction.

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I'll draw a big arrow there.

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I guess you could say that

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these things became even denser
in this outward direction.

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It is actually going to induce a current.

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And the current that it
will induce is going to go,

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is going to go in that direction

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and let me draw it a little bit clearer.

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The current is going to
go in that direction.

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It's going to go in a clockwise
direction around this.

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And that is because that
change in the magnetic flux

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that induces a voltage,

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an electromotive force that
causes this current to flow.

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That causes the current to flow

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and there's other ways to
change the magnetic flux.

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If I were to lessen the magnetic field

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in the outward direction or another way,

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if the change in the
magnetic field were inwards,

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then the current would
go the other direction.

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But the key here is when I change the flux

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through this surface defined by this wire,

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it's going to induce a current.

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The current isn't going to
be there if the thing is,

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if the magnetic field is stationary

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and I'm not changing this loop in any way.

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But as soon as I change
the flux in some way,

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I am going to induce a current.

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I could also instead
of changing the field,

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I could actually move my coil.

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I could move it that way.

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And if I were to move it that way,

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the flux going through this surface

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or I guess coming out of
this surface will increase.

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Because if I move this to the left,

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the magnetic field is denser,

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I guess it's stronger
so there'll be more flux

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through this area here.

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So, if you move it that way,

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you also would have a current like this.

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Now if you moved it the other way,

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if it was on the left hand
side and you moved it that way,

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it would also induce a current

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but now since the flux is lessening

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in the outward direction,

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the current would go in the other way.

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Now there's other ways to change the flux.

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You could actually change
the area of this actual loop

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if somehow it was made out of some

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maybe stretchy, stretchy wire somehow.

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If you increased its,

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if you would increase.

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Let me draw it this way.

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If you were somehow able to stretch it.

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Stretch it so it contains,

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so the actual area increases.

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If you were able to stretch it out

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so that the actual area increases

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which would cause the flux in the

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out of the screen direction
to increase even more,

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that also would induce,

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that also would induce the current.

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And so this whole idea of
a change in magnetic flux

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inducing a current, this is the essence

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and we'll go deeper into
it in future videos,

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this is the essence of Faraday's Law.

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Faraday's,

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Faraday's Law.

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And we'll quantify this
more in future videos

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but it's just the notion
that if I have a loop of wire

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and I have a changing magnetic flux

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through the loop of wire,

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that is going to induce
a current in that wire.