Eddy Current Demo

Conceptual Background

-eddy currents

 

-magnetic flux

-lenz’s law

 

 

Experiment

Materials:

• Aluminum plate
• 4 wooden rollers
• Permanent magnet

Procedure:

1. Lay the wooden rollers on a level table (evenly spaced- they will enable the aluminum plate to move)
2. Put the aluminum plate on the rollers
3. Move the magnet back and forth over the plate (without touching the plate)
4. Observe the motion of the plate in response to the moving magnet

 

What’s happening? 

1. Imagine that the aluminum slab consists of an infinite amount of eddy current loops. When the magnet passes over the aluminum slab, it’s magnetic field creates a magnetic flux through each imaginary loop.
2. As the magnet moves over the slab, the magnetic flux through each imaginary loop changes.
3. Because of Lenz’s law, the loops want to reverse this change to minimize change in flux, so a current is induced (seen in red) within the loops oriented such that a magnetic field is created which accomplishes this task.
4. This induced magnetic field (seen in red) counteracts the change in magnetic flux and acts like a permanent magnet, which then attracts (blue arrows) the permanent magnet, causing the aluminum lab to move across the table in the same direction as the permanent magnet, as it is temporarily magnetized through eddy currents and attracted to the permanent magnet.