Eddy currents: When a metallic plate is placed in a time varying magnetic field, the magnetic flux linked with the plate changes, the induced currents are set up in the plate; these currents are called eddy currents. These currents are sometimes so strong, that the metallic plate becomes red hot. In transformer frames there is a huge loss of energy due to production of eddy currents, so these currents are undesirable in transformer. 

Application of Eddy Currents: 

1. Induction Furnace: In induction furnance, the metal to be heated is placed in a rapidly varying magnetic field produced by high frequency alternating current. Strong eddy currents are set up in the metal produce so much heat that the metal melts. This process is used in extracting a metal from its ore. The arrangement of heating the metal by means of strong induced currents is called the induction furnace. 

2. Induction Motor: The eddy currents may be used to rotate the rotor. Its principle is: When a metallic cylinder (or rotor) is placed in a rotating magnetic field, eddy currents are produced in it. According to Lenz’s law, these currents tend to reduce to relative motion between the cylinder and the field. The cylinder, therefore, begins to rotate in the direction of the field. This is the principle of induction motion.