Physics Dept. Demonstration Manual

DEM44.0 - Eddy Currents

Objective:

To demonstrate the effects of the current induced in a non-magnetic conductor when the conductor passes through a magnetic field.

 
Apparatus:  
  • two Aluminum rings (one not continuous)
  • U-magnet (large, 13000 Gauss)
  • stand with upper pivot


Method:

A flat aluminum ring that is discontinuous (has a gap) is allowed to swing freely between the poles of a magnet. The ring swings unimpeded except for pivot friction.

The "gapped" aluminum ring is replaced with one having no gaps in its circumference. This ring is allowed to swing through the magnetic field. This time, the ring comes to a halt within two or three cycles. The eddy currents produced have been allowed to circulate around the ring, setting up an opposing magnetic field, which resists the motion (Eddy current braking).

One immediate implication is the construction of iron-cored transformers. The core is built up or laminated with thin sections of iron that do not allow a continuous flow of Eddy currents, transversely or circularly. Thus "Eddy current losses" are minimized.