Question

What are eddy currents? How are they produced? in what sense eddy currents are considered undesirable in a transformer? How can they be minimised? Give two applications of eddy currents.

Answer 1

Eddy currents: When a thick metallic piece is place in a time varying magnetic field , the magnetic flux linked with the plate changes, the induced currents are set up in the conductor, these currents are called eddy currents. These currents are sometimes so strong, that the metallic plate becomes red hot.
Due to heavy eddy currents produced in the core of a transformer, large amount of energy is wasted in the form of undesirable heat.
Minimisation of Eddy Currents: Eddy currents may be minimised by using laminated core of soft iron. The resistance of the laminated core increases and the eddy currents are reduced and wastage of energy is also reduced.
Application of Eddy Currents:
(i) Induction Furnace: In induction furnace, 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.
(ii) 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 tends 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.