hello I'd like to discuss and
demonstrate Faraday's law of
electromagnetic induction here we have a
statement of Faraday's law
electromagnetic induction known as
Faraday's law is that a changing
magnetic field or a changing magnetic
flux will create an electric field
Faraday first discovered this phenomenon
in the year 1831 he was over working at
the Royal Institution in London England and
he was working with some clothes of wire
and this is the discovery that he came
up with I'm now going to demonstrate
that he had a coil of wire on which he
wrapped his secondary coil which I'll do
here in just a minute
so that he had a primary coil which
would be like this yellow coil here and
he had a switch to connect it to a
battery then he had a secondary coil
connected up to a galvanometer so let me
go ahead and wire this up put the
secondary coil on it and we'll connect
it up and we'll do the experiment I see
what happens so now I'm prepared to wind
onto this primary coil a secondary coil
which is electrically independent from
it I have previously wound 200 turns on
the primary coil that's with this lead
and this lead being the ends of the
primary coil and now the secondary coil
is going to have this as one end and
when we cut that off we'll get to the
other end here I'm going to wrap 200
turns onto the secondary coil so I'll
wrap those turns 1 2 3 4 5 6 to 100 93
94 95 96 97 198 199 and 200 tons ok
we'll tie it off here at this point
then cut the end and clean the varnish
off of here
of course Faraday didn't have nice wire
like this he had to take copper wire and
wind it with string to keep the various
parts of the wire from shorting into one
another but we have an insulated wire so
the various parts of the coil are
electrically isolated from one another
but we need to clean the varnish off the
end of this to get a good connection so
now we have the coil in this fashion
primary coil we're going to connect up
the battery secondary coil we're going
to connect up to the galvanometer
the primary coil was wound on here first
it has 200 turns the secondary coil was
wound over the top of the primary it
also has 200 turns now I'd like to hook
up the circuit we're going to connect
the primary coil through the switch to
the battery one side and the other side
so that the the primary coil which was
the first coil wound on here 200 turns
will be connected when I throw the
switch to the battery the secondary coil
is the coil that's laid over the top of
the primary coil in this case and
that'll be connected to the galvanometer
which is a current detecting device now
the battery is going to pump electrons
through the circuit and when I throw the
switch it'll take just a fraction of a
second for that current to build up to
its maximum value it's that change in
current that will cause the changing
magnetic field that induces the electric
field in the secondary circuit which
causes a current to flow through the
galvanometer let's see what happens when
I throw the switch just when I throw the
switch I increase the current in the
primary circuit that causes a change in
the magnetic field which induces an
electric field which drives current
through the secondary part of the
circuit similarly when I open the switch
we will see another change in magnetic
field the magnetic field would drop to
whatever value it now
as to zero that to change in the
magnetic field and that causes a change
in the electric field in the other
direction which causes the current to
reverse its direction in a galvanometer
so when there's no change in the
magnetic field
there's no induced electric field in the
secondary coil and therefore there's no
current in the secondary coil there's no
change when the switch stays open or
when the switch remains closed no change
no change there's no effect but when
there's a change either opening the
switch or closing the switch we get a
change and the summarize a changing
magnetic field or a changing magnetic
flux will create an electric field
