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- [Voiceover] What I
wanna do in this video

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is give ourselves an introduction

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or an intuition for the
term Flux in general.

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And then think about how it applies

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to the idea of magnetic

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Magnetic Flux.

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So, first of all, when people
are just talking about flux,

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and this is the easiest way that I know

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how to conceptualize it.

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They're talking about
how much of something

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is flowing through a surface
in a given amount of time.

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So if you imagine that this is,

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this is, I'm just defining a
volume of air right over here.

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And let's say the air is
denser near the bottom

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of this volume of air,

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so there's more air down here

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than there is up here,

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which is generally true.

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Air density goes down as
you increase altitude.

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So there's very low density up here.

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This is in between.

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I don't have to draw
all the air particles,

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but you get the sense.

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Lot of air, lot of air down here.

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And the air is moving.

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And so let's say that the air,

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let's say the air is...

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Let me do the velocity
vectors in a different color.

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So, these are some of the
velocity vectors of the air.

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Let's say the air on this side is moving

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is moving at let's say, a medium velocity.

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So right over there.

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But as we move more in that direction,

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the air is moving faster.

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So they have larger
velocity vectors like that.

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We see that in general,
all of the air is moving

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in that general direction,
that's the way I'm drawing it.

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And I can draw the
velocity vectors over here.

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The air is less dense.

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But the trend in the velocity vectors,

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when I go from the left to the right is

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roughly the same.

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So that's the flow.

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Now I'm just sampling some of
the velocity vectors there.

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So let's talk about flux.

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And the thing about flux,

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really of any form,

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you have to think about a surface.

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So let's imagine you were
to put some type of a net.

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Let's say you were to put a net right over

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right over here, right over here.

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And if we think about the flux,

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we would say, well how much air

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is traveling through that net
in a certain amount of time?

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We could say how many molecules

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are traveling in say, each second.

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And so this would have some
flux associated with it.

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Relative to the air.

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But what if we were to take that same net.

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And we're assuming it's
some type of theoretical net

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that actually does not
impede the air flow.

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But it helps us visualize a surface.

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What if we were to move that
net a little bit to the right

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where the density is the same,

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but the particles are just moving faster.

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Well now, our flux would increase.

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So this is larger flux.

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Larger, larger flux.

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Why is our flux increase?

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Because, well, the density is the same,

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but in any given amount of time

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I'm gonna have more things
going through that surface.

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Now what if I were to put that same net

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and move it up to this high altitude,

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right over here?

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That high altitude.

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Well, the velocity of the
molecules are the same,

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and they're going in the same direction.

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But there's just fewer of them.

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So you're going to have
less fewer molecules

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traveling through the surface
in a given amount of time.

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So this is going to have smaller flux.

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And this is all relative to my first one.

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Smaller, smaller flux.

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Now, what if you were to take the same net

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and instead of the direction of the air

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being perpendicular to the surface,

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be normal to the surface,

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what if you were to take the net

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and reorientate it so
that the air is going

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in the same direction of the surface.

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So what if you were to take the same net

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and you were to make it like this.

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So that it's the same net.

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I know it doesn't look exactly the same.

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But it's the same net,

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and you're to make it like this.

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Well now how much air is
traveling through that net

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in a given amount of time?

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Well now very little to zero air

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is gonna be traveling through that net

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in any given amount of time.

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The air is going along the surface,

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not through the surface.

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So this one, let's just say that

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all the air is going exactly

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in the same direction as the surface,

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so nothing is going through the surface.

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We would say that this one has zero,

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zero flux.

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Now let's say that this theoretical net

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that actually does not
impede the air flow,

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let's say we can stretch
it or contract it.

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So if we stretch that net,

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in the same, let's say we were to do it,

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let's say we were to
stretch it up like this.

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So it becomes a bigger net.

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So it becomes a bigger net like this.

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Well now this thing's
gonna have larger flux

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because there's just more area.

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There's more to flow through.

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So now, if you said for this surface,

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you're gonna have a larger flux

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because there's just gonna be more air

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is going to go through that

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in any given unit of time.

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So as you can see,

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when we think about how much of something

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just flux in the traditional sense.

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How much of something
goes through a surface

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in a given unit of time.

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It depends in this case, the
density of the substance.

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It depends on

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it's velocity.

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Both the magnitude of the velocity

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and the direction of the velocity.

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We see if we orient the surface

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or if we oriented the velocity.

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So it's not going normal to the surface,

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perpendicular to the surface.

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Well then, we can have our flux go down.

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And you can have things in between.

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You can have a net.

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Let's say we took that same original net.

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But the direction of the
air is neither normal

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nor exactly in the same
direction of the surface.

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Well this flux is going to be in between,

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is going to be in between
that original flux.

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And this one right over here.

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There's gonna be air flowing through.

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There is going to be air

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flowing through

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the actual surface.

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But it's not going exactly
normal to the surface.

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And as we will explore later

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when we get a little
bit more mathy into it.

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We actually care about the component

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of the vector of the air
that is exactly normal

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when we eventually calculate flux.

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But this flux is gonna
be some place in between

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this one and the zero flux

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because the air isn't going
exactly perpendicular.

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Well that's just the more basic,

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or for me the more
intuitive notion of flux.

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But what do we mean by magnetic,

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by magnetic flux?

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Well, like regular flux,

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we're still dealing with
how things are kind of,

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you could say going through a surface.

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But instead of thinking
about air particles or

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water molecules or things like that,

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we're gonna be thinking
about a magnetic field.

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So let me draw a surface.

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So I have, I have a little bar magnet.

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This is the north side,
this is the south side.

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We see our field lines.

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And then I've drawn a
couple of the magnetic

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field vectors in white there.

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And let's say that we have a surface.

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We have a surface like this.

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And so, for this surface

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when we think about the flux

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we wanna care about...

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things are actually moving when
we think about magnetic flux

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we aren't actually thinking about actual

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physical things moving
through the surface.

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The way we did when we thought about,

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I guess you could say,
traditional or more,

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or flow-based flux.

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But it's a similar idea.

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We care about the component

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of the magnetic field.

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And the density of the magnetic field

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that is normal to this surface.

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So let's say that this has a given flux.

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So let's call that, and
the notation is phy.

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And, that's the flux
of the magnetic field.

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And once again, it's based on,

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it's based on the strength
of the magnetic field

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and specially the component
of the magnetic field vectors

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that are perpendicular,

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that are perpendicular
to this actual surface.

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So this would have one magnetic flux.

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But if I were to take the same surface

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and make it parallel,

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make it parallel to the
magnetic field vecotrs

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instead of being normal or...

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Now the magnetic field
vectors are parallel to it

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instead of being normal.

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So now our flux is zero.

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So this would have zero,
or pretty close to zero.

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So approximately zero

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magnetic flux.

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Magnetic flux.

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Flux.

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Now if I were to take this surface

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and instead of orienting this way

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I just moved it further away.

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So instead of putting in here

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I would take it all the way out here

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where the magnetic field is weaker.

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Where the magnetic field is weaker.

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So we have a weaker
magnetic field out here.

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The flux would also decrease.

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So it has a lot of the same properties

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as this more physical flux

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that we were talking about before.

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But instead of talking about, say,

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the velocity of the air molecules,

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no, the velocity vectors
of the air molecules

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and how those relate to the surface,

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here we're talking about
the magnetic field vectors.

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And how those relate to the surface.

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But the metaphor, the
analogy is still the same.

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If they are perpendicular,
you have larger flux.

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If they are going in the same direction,

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you might have zero or very little.

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You might have very little flux.

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If you have a weak
magnetic field out here,

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the flux is going to be lower

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than if you have a strong magnetic field.

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That's analogous to,

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when you had high density
and high velocity,

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that was a lot of flux.

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Versus low density or low velocity

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that is lower flux.

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And also, we can increase
the total surface.

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So if we stretch that surface

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or we had a larger
surface right over here,

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the flux through this
surface is gonna be larger

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than the flux through this surface.

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Let's say this surface is analogous

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to a surface like this right over here.

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Let's say that the magnetic
field is symmetric on both sides

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so the flux through this surface

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and this surface would be the same.

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So if you were to stretch it out

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to be a larger surface,

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well now you just have
more of the magnetic field

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that is now normal to the surface.

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So hopefully this gives you
at least a beginning ideas

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of the notion of magnetic flux.

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And how it relates to,

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I guess you could think
of more physical flux.