Faraday's Law Introduction

- [Voiceover] In other
videos we talk about

how a current flowing through a wire

can induce a magnetic field.

And we're going to talk
about in this video

is how we can go the other way.

How a change in a magnetic field

can affect or induce a current

in a loop of wire.

So we're gonna be going from a change,

change in and actually we're gonna

focus on magnetic flux.

Magnetic flux through a loop.

Through a loop.

And we're going to see how this

actually induces a current in that loop.

So it induces a current.

Induced current.

So this right over here,

and this is my attempt at
drawing a magnetic field,

and these are the magnetic field lines.

They don't look like lines because

they're all popping out of the screen.

They're moving towards
you, towards the viewer,

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

And there's different ways
of showing magnetic fields.

You could show magnetic
field lines like this.

You could also use vectors.

And when you're using field lines,

it's the density of the field lines

tell you how strong the magnetic field is.

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

And so the magnetic field is less strong

on the right-hand side over here

than they are on the left-hand side,

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

Now if we did it with vectors,

we would have a bigger arrows pointing out

over here than we would over there.

But now let's do a loop of,

let's do a loop of wire.

So let me draw a loop of wire here.

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

so this is my loop of wire.

My loop of wire.

So if I just throw that loop of wire,

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

and the magnetic field isn't changing,

I do have some flux
going through the I guess

you could say the surface
defined by this wire,

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

I encourage you to watch
the video on magnetic flux.

But if I just have this wire stationary

in the magnetic field
nothing is going to happen.

But I will be able to induce a current

if I change the magnetic flux

going through this surface in some way.

So for example, right
now the magnetic field

is pointing out of the screen.

If I were to make it even stronger

than the direction
pointing out of the screen,

so I guess one way to think about it is

if the change in the magnetic field,

the change in the flux were to get

even stronger in the outward direction,

so I don't know a good way to,

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

I'll draw a big arrow there,

I guess you could say that these things

became even denser in
this outward direction,

it is actually going to induce a current.

And the current that it will induce

is going to go in that direction.

And now let me draw a little bit clearer.

The current is going to
go in that direction.

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

And that is because that change

in the magnetic flux
that induces a voltage,

an electro mode of force

that causes this current to flow,

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

If I were to lessen the magnetic field

in the outward direction or another way,

if the change in the
magnetic field were inwards,

then the current would
go the other direction.

But the key here is when I change the flux

through this surface defined by this wire,

it's going to induce a current.

The current isn't going to be there

if the magnetic field is stationary

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

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

I am going to induce a current.

I could also, instead
of changing the field,

I could actually move my coil,

I could move it that way.

And if I were to move it that way,

the flux going through this surface,

or I guess coming out of
this surface, will increase.

Because if I move this to the left,

the magnetic field is denser,
I guess it's stronger,

so there will more flux
through this area here.

So if you move it that way,

you also would have a current like this.

Now if you moved it the other way,

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

it would also induce a current,

but now since the flux is lessening

in the outward direction,

the current would go in the other way.

Now there's other ways to change the flux.

You could actually change the area

of this actual loop if somehow it was made

out of some maybe stretchy wire somehow.

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

If you were somehow able to stretch it,

so it contains, so the
actual area increases,

if you were able to stretch it out

so that the actual area increases,

which would cause the flux in the out

of the screen direction
to increase even more,

that also would induce the current.

And so this whole idea of a change

in magnetic flux inducing a current,

this is the essence and we'll go deeper

into it in future videos,

this is the essence of Faraday's Law.

Faraday's Law.

And we'll quantify this
more in future videos,

but it's just the notion

that if I have a loop of wire,

and I have a changing magnetic flux

through the loop of wire,

that is going to induce
a current in that wire.