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Hi! Let's have some fun with eddy currents.
The standard experiment for showing eddy currents is a non-magnetic
copper tube and a neodymium magnet.
The magnet will fall very slowly through the tube
because of the induced eddy currents in the copper.
These currents have their own magnetic field that reacts with the magnetic field of the magnet
in a way that slows down the magnet.
But this experiment has a flaw:
people often think it is just trapped air and friction that is slowing the magnet down and I
can understand why some people think that this is the case.
Take a look at this lens assembly from an old laser device.
The lens is dropping very slowly but there are no magnets, eddy currents or
motors in this. It's just trapped air slowly seeping out in the very small gap
around the lens.
So let me show you the eddy currents' effect in another way. This time with an
aluminium profile and a small stack of neo- dymium magnets from an old hard disk drive.
No trapped air but it still could be confused with friction although a piece
of iron falls very quickly compared with the magnet.
In real life you can feel a drag on the magnet from the eddy currents.
Let me try to visualize it using a magnet with a rubber band around
it and five kilos of copper.
On the table there's a little friction but the magnet just follows my hand.
Now watch for the eddy currents in the copper...
I think you saw the drag.
Next you have to listen for how the eddy currents brakes the magnet's fall.