Faradays Law - Electromagnetic Induction, Physics Video Lecture - Class 12

hi there it's Steven Williams again from
open up in college and they're talking
some more about electromagnetism and
it's just in particular today what I
want to talk about is Faraday's law I
mean after Michael Faraday one of the
earlier expense if earlier experiment is
electricity and magnetism and you have a
picture of him here and it was for
Michael Faraday that the fare ad was mu
the unit of capacitance and actually
you're taking a long time to figure out
where the farad was named who it was
named after and it was only a couple
years ago actually that I figured
figured that out now I'm not gonna tell
me what Faraday's law is yet
I'm going to show you a couple of
animated experiments now this is from
the Phet web coach and you can find all
sorts of great physics animations and
science animations on the Phet web page
this one in particular is demonstrating
Faraday's laws and this is this one's
called Faraday's electromagnetic lab
that's slight here do that for so bring
that down here's the website to
Faraday's today's law loud today's you'd
like to magnetic club so you can take
that website down and check it out
yourself and play around if this kind of
suggesting the flame of it see what kind
of different effects you can get anyway
let's go back to you the actual lab
itself so what we've got here is a
permanent magnet look north himself and
we can see the magnetic field that's
created from my magnet around there in
the street here inside the magnet we've
got a loop of wire to which I'm life
over the patch well here is a
demonstration of Faraday's law
what you'll notice is I move the magnet
and the light turns on and in particular
when I move the magnet notice what's
happening with the magnetic field it's
changing so Faraday's law says that if
you have a changing magnetic field that
is going to induce a voltage in this
case we better complete a circuit so
it's going to induce a current in a
circuit and that light bulbs going to
turn on if something else is kind of
interesting
okay I've got three loops curling and
I've got I've got leaves off the screen
but I can change the number of roots to
give it to one and take it
look at the light bulb as I change it
when you change it now and now and
you'll notice that the light bulb turns
on as I change the number of loops in
death and also if I change the area of
Marcel I phone turns on just very clear
very briefly very doing as I change the
area that the magnetic field or the area
with the magnetic field passes through
so basic fundamental underlying equation
for Faraday's law is this if you have
the changing magnetic field that is
going to induce a voltage in particular
to change in flux respect to time so the
induced voltage is going to be equal to
the rate of change of the flux with
respect to time times how many loops you
have another way to write this if we
remember what flux is and we we actually
write flux in terms of flux density so
flexi going to equal to flux density
times area
and time in flux density times area is
equal to flux so what we can what we you
can see from this equation here is if
you have a changing magnetic field you
will induce a voltage or if you have a
changing area you will induce a voltage
or if you have both we can go back to
that paramagnetic Faraday's law and see
here's the changing magnetic field
induces a voltage with pigs okay or the
shift is over a little bit vector tech
and change the loop area and make you
mean weak area it doesn't work quite it
doesn't seem to cut is love is enough
the magnitude of the changes in physics
O'Keefe but you can see if I'm changing
it quickly enough that the light bulbs
light up very briefly now this is all
sorts of useful applications and the
most useful application is going to be
in generator
you know cartoon of a generator here we
turn on the tap this magnets gonna spin
was going to create a changing magnetic
field a changing magnetic field is going
to turn that light bulb off
that's all men AC generators and you can
see the I change the area of API change
in I just can't see it leg up to my
fellow you go increasingly done way up
to my increasing it it does if I change
the loot day from a hundred percent
look just like this over all that normal
and percent down to 92 very but let's
light that the foursome now you can see
I'm changing the area so I'm going back
to the equation here for da DT the areas
to me with respect to time I'm going to
reduce the voltage which in this example
is going to create a clear and that is a
Faraday's law