When a changing magnetic flux acts on a bulk conductor, closed circulating currents are induced within the material itself. Because the conductor path can have low resistance, these currents may become large and convert energy into heat.

• They are called eddy currents because their circulation resembles eddies in water.
• The current loops are internal to the conductor and do not need a separately drawn wire circuit.
• Trap: mistaking eddy currents for desired transport current rather than induced loop currents inside the body.

Eddy-current loss is reduced by increasing the resistance path available for circulation. The textbook methods are lamination and slotting, both of which weaken the current loops and therefore reduce heating and excessive damping.

• A solid core allows stronger eddies because the conducting path is broad and continuous.
• A laminated core breaks the path and makes current circulation harder.
• Trap: thinking lamination changes the source of magnetic flux; its main role here is to reduce the unwanted current loops.

Although eddy currents usually waste energy, some devices use their heating or retarding effect deliberately. The chapter lists dead-beat galvanometer, electric brakes, induction furnace, speedometer, and energy meter as standard examples.

• Dead-beat galvanometer uses eddy-current damping so the pointer settles without oscillation.
• Electric brakes and speedometers use the retarding effect associated with induced currents.
• Induction furnace uses Joule heating by eddy currents to melt metal.