Eddy Currents and Braking
Eddy Currents and Braking
- A changing flux through a solid conductor can drive closed current loops inside the metal. These loops are called eddy currents.
From changing flux to a braking force
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- Different parts of the rotating disc enter and leave the magnetic field, so the flux through those parts changes.
- Induced current loops form inside the conducting disc.
- Their magnetic force produces a torque opposite to the rotation.
- The disc loses kinetic energy. Electrical resistance transfers this energy to thermal energy.
- Faster motion gives a larger rate of flux change, larger eddy currents and stronger braking.
- Slots or insulating layers break the current paths and reduce eddy currents when heating is unwanted.
Your turnapplication check
A solid metal disc and a disc with radial slots rotate at the same speed through the same field. Which has the weaker eddy-current braking, and why?
Show worked answer
The slotted disc has weaker braking. The slots interrupt the closed current loops, so the eddy currents and their opposing magnetic torque are smaller.