# Faraday’s Law Introduction | Physics | Khan Academy

– [Instructor] In other
videos, we talk about how a current flowing through a wire can induce a magnetic field. Now what 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. We’re gonna be going from a change, change in, and actually we’re
gonna focus on magnetic flux. Magnetic. Magnetic flux through a loop. Through a loop. Now we’re going to see how this actually induces a current in that loop. So, induces. Induces a current. Induced current. This right over here, all right, this is my attempted
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 could view these
as the tips of the arrow. Now 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. If you got 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 bigger arrows
pointing out over here than we would over here. But now let’s do a loop of, let’s do a loop of wire. Let me draw a loop of wire here. Let’s say I have a loop of wire that is, this is my loop of wire. My loop of wire. If I just throw that loop of wire and if 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 can 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 in the direction pointing
out of the screen. So, I guess one way to think about it is if I were to, 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, just gonna get even stronger
in the outward 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, is going to go in that direction and let me draw it 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 electromotive force that
causes this current to flow. That causes the 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 thing is, 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’ll be 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, stretchy wire somehow. If you increased its, if you would increase. Let me draw it this way. If you were somehow able to stretch it. 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, 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, 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.

## 50 thoughts on “Faraday’s Law Introduction | Physics | Khan Academy”

• ### TKO593 Post author

Conductor+magnetic field+relative motion=induced current. You should do more electrical engineer videos.

• ### krozz Post author

pls do more of this. I need to learn more about electrical engineering for robotics club

• ### The Flagged Dragon Post author

Will later videos have Maxwell's equations in them?

• ### CrystalMath Post author

Thank you for this video.

Thanks!

• ### TheGrumpySock Post author

are this the new videos because I see there areย  older ones?

• ### DarkDarkington Post author

Does anyone know what program he uses to do this?

• ### Passwordcracks Post author

this makes no sense

• ### Joshua Park Post author

yes, please do more on electricity and magnetism. thank you

• ### Halil Gunesli Post author

Great timing ,I'm taking electricity and magnetism and it's great to see you explaining these topics thanks.

• ### RAHIMI RASIP Post author

to keep unducing current, do we need keep changing the magnetic flux through loop?

• ### Kapilan Satkunanathan Post author

I was about to drop the course then i saw this video thanks ๐

• ### Kavin Timothy Post author

Hi i don't really get emf and pd, can you explain that?

• ### Savannah Patterson Post author

Isn't the current actually going in the counterclockwise direction? If you use the right hand rule and point your thumb toward yourself in the direction of the magnetic field, you would curl your fingers in the counterclockwise direction, right?

• ### Too Much Candor Post author

His digital handwriting is still better than my real handwriting…,,,

• ### Zain Ahmed Post author

Great work Sal

• ### Project Hu148 Post author

why does "CHANGE" in magnetic flux induced a current?

• ### Saรบl Post author

My cancer has just been cured

• ### Chief of mischief Post author

its good if u r speaking slow bcz we r from dfrnt countries

• ### hery sd ree Post author

sorry I still dont' understand how to determine the direction of current why it is clockwise?
is that " out of paper " means the current has to be clockwise ?

• ### Doom Doom Post author

If the magnetic field is uniform and the wire loop is moving at a constant velocity in the field, there will be no e.m.f induced in this case. Is this right?

• ### 17joren Post author

Is the emf induced pointing upwards to be perpendicular to the B field coming out of the board? Does it conflict with the current flowing down on the right side of the wire?

• ### Andre Dean Post author

this is why I can't make a wirless charger

• ### Kalyph Dioquino Post author

Where are the equations?

• ### harsh savla Post author

not very well explained, unfortunately

• ### DRAIN FISH Post author

How does inducing an emf cause a current to be induced

• ### แฟ ฬฯฮฟฮบฯแฟฯฮฎฯ Post author

Shouldn't the current be going anti-clockwise to begin.
Field is coming out the plane so right hand rule??

• ### MEKKANNOID Post author

This video made me hate the word 'change'

"chyaaaaange"

• ### Abdullah Mohamed Post author

Arabic captions pls

• ### Sahil sharma Post author

Exam not fear is so best

• ### Omar El-Yarakany Post author

In a previous video you showed the direction of current using the right hand rule indicating that it has same direction of the force, but when you increase magnetic flux i cant figure out the direction of force that creates the current

• ### Henry Esparza Post author

Gauss but with electromagnetism got it

• ### Petakyah Buckley Post author

You suck at explaining use simpler words and easier to understand examples

• ### Anton Sandaruwan Post author

Great lecture

• ### Daniel Kreipke Post author

In observing the cross section of a magnetic field:
– if the flux is increased in an anterior direction, a clockwise current is induced
– if the flux is increased in an posterior direction, a counter-clockwise is induced

• ### Ruhit Abdul-Qahhar Post author

Why is current not anticlockwise??? Isn't he using the right-hand grip rule?

• ### The Mad Cow Post author

convoluted explanation

• ### Ankit Jain Post author

Why do chane in magnetic flux created a induced EMF?

• ### Keen Observer Post author

Why is there no induced current to begin with? The Flux isn't = 0, you only have magnetic field lines going one way and none going the other way. I understand that a change in flux induces a current, but you allready have flux to begin with, so what's going on? I feel like this topic isn't explained very well by most people.

• ### Caleb Rossouw Post author

I'm writing tomorrow help

• ### Jonathan Kiing Post author

what happens when you have a loop (with no external voltage applied) inside of an unchanging magnetic field?? will there be current induced in the loop?

• ### Ray Tindell Post author

Those are electrons. Current is the flow of electrons

• ### Double Orts Post author

goodman thanks!

• ### Jenny Post author

Sorry i dont get it

• ### shellwhale Post author

So basically, the more smooth the more current am I right ?

• ### Ryan Marshall Post author

@ 2:53 – why does the current go clockwise?

• ### thrupthi ganiga Post author

I always turn to khan academy videos for better understanding of basic topics, it would be of great help if you have engineering topics too

• ### Michael La Moreaux Post author

Only when the magnetic field intrinsically changes does it cause an emf in the coil. Any change in the flux due to motion of the coil has no effect; the emf is produced by the motion of the wire through the magnetic field. Faraday's Law obfuscates the principle involved.

• ### Minakshi Thakur Post author

๐๐๐๐๐๐๐๐๐

• ### A tired Soul Post author

How can i know how many lines pass through the loop ring