Question

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

Answer 1

Hint: The question demands us the definition and generation of eddy current. Eddy currents are produced in case of a working transformer. This causes loss in the efficiency of the transformer. Remind the definition of eddy current and how you would minimize its effect in a transformer.

Complete answer:
Eddy current is the effect of electromagnetic induction. Let’s define it first and then we will move on to its generation and how it affects the transformer.
Eddy current may be defined as: the current induced in the body of a thick metallic block when placed in a changing magnetic field. In other words it is an effect of electromagnetic induction.
Let’s consider a thick metallic block placed in a changing magnetic field whose north-pole is facing towards a metallic block.

When a changing magnetic field passes through the block, magnetic flux linked with the body of thick metallic block changes. This changing magnetic flux induces a current in the block. Due to low resistance as the block is a thick metallic block, induced current is very high and according to Lenz’s law induced current looks like concentric circles. So such a current is called eddy current.
Let’s now move to the construction of the transformer. A transformer consists of two coils wrapped around a single metallic core. If the core of the transformer is thick this will reduce eddy current in the core.
Thus in order to minimize the eddy current loss or to increase the efficiency of the transformer, we use a laminated core. Lamination of the core means, the core is made up of insulated layers of iron 'glued' together.

Applications of eddy current:
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 produce so much heat that the metal melts. We use this in metal extraction from the ore.

Induction Motor: The eddy currents may be used to rotate the rotor. 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. Due to this the cylinder begins to rotate in the direction of the magnetic field.

Note: This is a theoretical question. The student needs to learn the basic fundamentals of electromagnetic induction. This question depends on the statement of Lenz’s law. Its general statement is: The direction of induced current should be such that it opposes the very cause which produces it.