Q.1 What are Eddy currents?  Give its two uses.

Ans:- Whenever the magnetic flux linked with a metal sheet or block changes, an emf is induced in it. The induced currents flow in closed paths in planes perpendicular to the lines of force throughout the body of the metal. These currents look like eddies or whirl-pools in water and so they are known as eddy currents.

Use of eddy currents: Although eddy currents are undesirable, they still they find uses in the following devices:

1. Induction furnace: If a metal specimen is placed in a rapidly changing magnetic field (produced by high frequency a.c.), very large eddy currents are set up. The heat produced is sufficient to even melt the metal. This process is used in the extraction of some metals from their ores.

2. Electric brakes: A strong magnetic field is applied to the rotating drum attached to the wheel.  Eddy currents set up in the drum exert torque on the drum so as to stop the train.