Pendulum Damped due to Eddy Currents
A solid metal plate swinging between the poles of a magnet stops in a couple of swings, while a slotted plate keeps going. This simulation shows the induced current loops inside the metal that cause the difference, and lets you switch between plate types to compare.
How to use this simulation
- Switch between a solid plate and a slotted or combed plate
- Change the magnetic field strength
- Set the starting amplitude of the swing
What to look for
- The solid plate loses amplitude dramatically faster than the slotted one
- Eddy currents are strongest as the plate crosses the edge of the field, where flux changes fastest
- Damping increases sharply with field strength, since the induced current scales with it
The physics behind it
As the plate enters and leaves the field the flux through it changes, inducing circulating eddy currents. By Lenz's law those currents oppose the change that produced them, so they create forces that resist the motion, converting the pendulum's kinetic energy into heat. Cutting slots in the plate breaks the current loops and the damping largely disappears.