Question

(a) How are eddy currents generated in a conductor which is subjected to a magnetic field?
(b) Write two examples of their useful applications.
(c) How can the disadvantages of eddy currents be minimized?

Answer 1

Eddy currents are basically the currents that are induced in a body of the given conductor due to the change in the magnetic flux in which the conductor is kept.
The magnitude of eddy current is defined as
$I =$ induced e.m.f. / resistance
$I = \dfrac{e}{R}$
But induced e.m.f. is the rate of change of magnetic flux i.e.
$e = \dfrac{{ - d\phi }}{{dt}}$
where $d\phi =$change in the magnetic flux, $dt =$ change in time in which flux is changed
So, $I = \left( {\dfrac{{ - d\phi }}{{dt}}} \right)\dfrac{1}{R}$

Complete step by step solution:
(a) When a conductor is subjected to the time varying magnetic field then the change in the flux due to the relative motion of the field and conductor induces current in the conductor. Because of the conduction electrons, induced current flows through small loops which were created because of varying magnetic fields.

(b) Eddy currents are useful in many ways and some of them are as given below-
i) Induction Furnace: It is used to produce high temperature in preparing alloys by melting the constituent metals.
ii) Eddy currents are also used in deep heat treatment of the human body which is known as dia-thermy.

(C) The disadvantages of the eddy current can be minimized by taking the core of induction (that is metal core) in the form of thin sheets. The planes of these sheets are arranged parallel to the magnetic field so that they cut across the eddy current path.

Note: 1. The flow pattern of eddy currents resembles swirling eddies in water. These were discovered by Foucault in the year 1895 hence they are also called Foucault currents.
Eddy currents in the given conductor can be reduced to some extent, but cannot be eliminated.
2. The direction of eddy currents can be obtained by Lenz’s law or Fleming’s right-hand rule.