Eddy currents

Electric currents created in a steel component held in an alternating electro-magnetic field.

When an electric current passes through a wire, a magnetic field is created around the wire. If the electric current is alternating, the magnetic field collapses and grows in the opposite direction with each cycle. If the wire is made into a coil and a steel bar is inserted into it, the continually growing and collapsing field causes (or induces – hence induction heating) eddy currents to flow in the bar and thereby heat it up.

See also induction heat treatment.