We have seen that whenever the flux, linking with a closed electric circuit changes, an EMF has induced in the circuit and a current flow, the value of which depends on the emf around the circuit and the resistance of the circuit. It is not necessary that the circuit be a wire and that the flux passes entirely through it.
If a solid block of metal is traversed by varying flux, metallic circuits in the block itself, which are linked by the flux, will carry current. If the magnetic circuit is made up of iron and if the flux in the circuit is variable currents will be induced by induction in the iron circuit itself. All such currents are known as Eddy Currents.
Eddy currents result in loss of power, with consequent heating of the material. The magnitude of power loss due to eddy currents is often a matter of considerable importance in electrical engineering.
Electrical machinery usually involves varying fluxes. In DC as well as AC machines, we have an armature built of iron. In a permanent magnetic field or through which a revolving magnetic field passes.