• word_count: 200

Eddy currents — circulating currents induced in bulk conductors by changing magnetic flux — have both useful and detrimental effects. They follow Lenz's law, opposing the change that created them.

Useful applications: (1) Electromagnetic braking — eddy currents in a metal disc near magnets create a retarding torque proportional to angular velocity. Used in trains, laboratory balances, and roller coasters. (2) Induction furnace — rapidly alternating field induces large eddy currents in metal, heating it to melting temperatures. (3) Dead-beat galvanometer — eddy currents in the metal frame quickly damp oscillations. (4) Induction cooktop — high-frequency eddy currents in ferromagnetic vessels produce direct heating. (5) Metal detectors — eddy currents in nearby metal objects alter the search coil's inductance. (6) Speedometer — rotating magnet induces eddy currents in an aluminum drum, producing a torque proportional to speed.

Detrimental effects: in transformer cores and motors, eddy currents waste energy as heat. Mitigation: laminated cores (thin insulated sheets perpendicular to expected eddy current paths increase resistance). Eddy current power loss $\propto f^2 B^2 t^2$ (where $t$ is sheet thickness), so thinner laminations and lower frequencies reduce losses.