Magnetic Breaking

Magnetic Braking: Finding the effective length over which Eddy currents form

The magnetic Braking is a form of braking so popular now that even Millennium Force, Cedar Point’s new 92 mph rollercoaster, uses it this system as opposed to the traditional friction brakes. Magnetic braking works because of induced currents and Lenz’s law. If you attach a metal plate to the end of a pendulum andlet it swing, its speed will greatly decrease when it passes between the poles of a magnet. When the plate enters the magnetic field, an electric field is induced and circulating “eddy currents” aregenerated. These currents act to oppose the change in flux through the plate, in accordance with Lenz’s Law. The currents in turn dissipate some of the plate’s energy, thereby reducing its velocity.
Inorder to work properly, the eddy currents need a place to form. It can be seen that when cutting slits in the plate, the damping force caused by the magnet decreases.
Cadwell, an accreditedphysicist, has experimentally determined this effective length over which the currents form to be slightly less than the effective vertical height of the magnetic field.

As I told you before, for ourexperiment, we are interested in the braking of a rectangular sheet moving linearly through the magnet. Cadwell is a good source for explaining why this braking happens.
This picture shows the LorentzForce experience demonstrating the “eddy currents” form, explaining when a metal moves on the presence of a magnet its electrons will move.

The experiment
In this experiment, they chose a modelresembling a roller coaster to explore the aspects of magnetic braking.
And they decided to use a square copper plate attached to a cart which moves along a track underneath a magnet. When the platepasses between the poles of the magnet, the field induces eddy currents in the plate.

In order to test the behavior of magnetic braking, the same test was performed while varying the number of slots...