| Visualizing EM | Vector Fields | Electrostatics | Magnetostatics | Faraday's Law | Light | Notes | Copyright |
TEAL Electricity & Magnetism

SECTION : Falling Magnet  

SUBJECT: Magnet Falling Through a Conducting Ring  
see a distant view of this experiment  

A magnet is dropped through a conducting cooper ring. As the magnet falls under gravity, a current is induced in the ring that tries to keep the magnetic flux through the area of the ring constant. This corresponds to a field that produces a force that opposes the motion of the magnet: as it approaches from above, and the induced current generates a field that pushes the magnet upwards from below.

Once the magnet falls through the ring, the direction of the induced eddy current changes to produce a field that tries to pull the magnet upwards from above. Since the resistance of the ring is finite and the magnet is heavy, the flux through the ring does not stay constant, and the relatively small magnitude of the induced field does not generate a force strong enough to prevent the magnet from falling through.

The film shows this experiment being conducted in real life. The magnet is a very strong rare earth magnet. In order to make this phenomena easily observable, the copper ring has been cooled in liquid nitrogen to bring down its resistivity.




640x480 version