WEBVTT

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- [Voiceover] 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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And 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

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in a loop of wire.

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So we're gonna be going from a change,

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change in and actually we're gonna

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focus on magnetic flux.

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Magnetic flux through a loop.

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Through a loop.

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And we're going to see how this

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actually induces a current in that loop.

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So it induces a current.

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Induced current.

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So this right over here,

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and this is my attempt at
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 because

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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 can view these as
the tips of the arrow.

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And 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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So if you go to the right
here, they are less dense.

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And so the magnetic field is less strong

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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 a bigger arrows pointing out

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over here than we would over there.

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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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So let me draw a loop of wire here.

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

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so this is my loop of wire.

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My loop of wire.

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So if I just throw that loop of wire,

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and it 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 I guess

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you could 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 stationary

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in the magnetic field
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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than 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 the change in the magnetic field,

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the change in the flux were to get

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even stronger in the outward direction,

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so I don't know a good way to,

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so it's gonna get even stronger
in the outer direction,

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I'll draw a big arrow there,

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I guess you could say that these things

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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

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is going to go in that direction.

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And now let me draw 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

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in the magnetic flux
that induces a voltage,

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an electro mode of force

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that causes this 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

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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,
I guess it's stronger,

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so there will more flux
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

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of this actual loop if somehow it was made

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out of some maybe stretchy wire somehow.

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If you had increased,
let me draw it this way.

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If you were somehow able to stretch it,

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so it contains, 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 out

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of the screen direction
to increase even more,

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that also would induce the current.

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And so this whole idea of a change

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in magnetic flux inducing a current,

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this is the essence and we'll go deeper

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into it in future videos,

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this is the essence of Faraday's Law.

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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

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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.