Eddy Currents (Magnetic Braking)

Eddy currents are circulating currents induced in a BULK conductor whenever flux through it changes — not in a wire loop, but in the material itself.

By Lenz's law, they always flow so as to oppose the change in flux — producing a force or torque that resists the motion or change creating them.

They dissipate energy as heat (I²R), which can be a loss or a feature depending on context.

Bad eddy currents: in transformer cores, motor armatures, induction-coil bodies — energy is wasted as heat. Mitigation: LAMINATE the core into thin insulated sheets so eddy paths are short.

Good eddy currents: induction cooktops (heat pots directly), electromagnetic brakes (no contact, no wear, smooth braking), metal detectors (sensing induced eddies), induction furnaces.

A swinging metallic plate between magnet poles is heavily damped by eddy currents — its kinetic energy is converted into heat. Slot the plate and the damping disappears.

Power dissipated by eddy currents in laminated cores scales as (B·f·t)² where t = lamination thickness, so thinner laminations dramatically reduce losses.