Fun With Eddy
Current
Eddy Current
An eddy current is a circular electric current induced inside a conducting material when the magnetic field around or through that material changes. Unlike current in a wire, which travels along a defined path, eddy currents swirl within the body of a metal such as copper, aluminum, or iron.
They are an important effect of electromagnetic induction and are useful in many technologies, although they can also cause unwanted energy loss as heat energy.
Let us perform a few simple fun-experiments to demonstrate the presence of eddy current.
If you would like to read more about eddy current, please read this post on eddy current.
Effect of Eddy Current
Eddy currents themselves are not usually visible, but we can observer their effects easily.
A strong magnet falling through a copper or aluminum tube falls much more slowly than it does through a plastic tube. The falling magnet results in changing magnetic flux. And this change in magnetic flux cause eddy currents, in the copper tube, which resists the magnet’s motion. This opposition produces magnetic braking of the magnet.
Experiment to Demonstrate
Eddy Current
This simple experiment demonstrates that a changing magnetic field can produce eddy currents in a conductor.
Materials needed: A strong cylindrical magnet, a copper tube, and a plastic tube of similar size.
Hold the plastic tube vertically and drop the magnet through it. Observe that the magnet falls quickly. As you can observe, it takes about half a second to fall through the 5 feet plastic tube.
Now hold the copper tube (5 feet long as the plastic tube) vertically and drop the same magnet through it.
Observe that the magnet falls much more slowly through the metal tube. It almost takes 6 or 7 seconds to fall through the copper tube of 5 feet long.
Explanation
As the magnet moves through the metal tube, the magnetic flux through different parts of the tube changes. This induces eddy currents in the tube. The magnetic field produced by these currents opposes the motion of the falling magnet, so the magnet slows down. In the plastic tube, no significant eddy currents are produced because plastic is not a good conductor.
Conclusion
Eddy currents are an important effect of electromagnetic induction. When the magnetic field near a conductor changes, it induces eddy currents that oppose the change that created them.
Eddy current is responsible for a magnet to fall slowly in a copper tube as we demonstrated.