In 1831, Michael Faraday in London and Joseph
Henry in New York independently discovered
electromagnetic induction.
I am going to demonstrate electromagnetic
induction with an experiment similar to the
one Michael Faraday performed.
I have an ammeter here and I have three coils.
I have a coil with one loop, ten loops, and
100 loops.
I also have a bar magnet and I will start
by connecting the single loop coil to the
ammeter.
I now have the single loop coil connected
to the ammeter and I'm going to move the bar
magnet into and out of the coil.
And, if you watch very closely, you can see
a slight deflection of the ammeter needle.
Ok, so now let me connect the ten loop coil.
And then I'm going to do the same thing.
I'm going to move the bar magnet in and out
of the coil.
Now you can see more movement of the needle.
In fact, if I go very slowly you see just
a little bit of a deflection, and if I go
quickly you see a greater amount of deflection.
Also, as the magnet is going in the needle
deflects to the right.
And as I pull the magnet out, it deflects
to the left.
But when the magnet isn't moving, there's
no deflection, indicating no current flowing.
Ok, so when the magnetic field is changing
going into the coil, there's a positive current
flowing.
When it's changing, coming out of the coil,
there's a negative current flowing.
And now let me connect the 100 loop coil.
And I'll start by moving the magnet in very
slowly.
You see a deflection to the right; pull it
out, to the left.
If I go in quickly, you see a much greater
deflection.
Ok, so the rate of change of the magnetic
field affects the current, also.
the current, also.
