Question

In which of the following devices, Eddy current is not used?
A). Induction furnace
B). Magnetic brake in train
C). Electromagnet
D). Electric heater

Answer 1

Hint: According to Faraday’s law, when we change the magnetic field in the conductor, loops of electric current are induced within the conductors. These loops are called Eddy Currents. They are also called Foucault's currents. These currents have an efficiency of $100\%$.

Complete step-by-step solution:
Mechanical brakes are based on friction. But, magnetic brakes have Eddy current. Brakes have a disc which rotates perpendicular to the magnetic field. As the disc rotates, Eddy currents are induced. Then power is dissipated throughout the disc which produces a braking torque.
Eddy current effect is used in the electromagnets are widely used. An example of this can be the ordinary electricity meter in every house. Eddy currents make the aluminum disk in an electricity meter to spin. Then this number of spins or revolutions shows the usage of electricity.
In an Induction furnace, a coil carrying AC surrounds the chamber of metal. Eddy currents are induced in the metal. The circulation of these currents generates high temperature which is used to melt metals. After melting, these melted metals are mixed to make alloys of the same composition.
Electric heaters produce heat. They take all the energy and supply it in the form of heat. Eddy current has an efficiency of $100\%$ which means it gives all the energy to do the work. So much heat cannot be used in electric heaters.
Thus, Eddy current is not used in an electric heater.
Hence, the correct answer is option D i.e. electric heater.

Note: Eddy currents are used to heat artifacts and can also be used to find defects and cracks in metal using eddy-current test devices. Eddy currents may produce resistive forces. Then these forces change energy from one form to another. Heat and electromagnetic forces can be generated in a conductor because of these Eddy currents.