Question

Which of the following appliances does not use electromagnets?
A) Fan
B) Electric bell
C) Radio
D) Heater

Answer 1

Hint: Concept of electromagnet :- electromagnets are devices used to create magnetic fields using electric current, mostly by using a wired wrapped around in the form of a coil on a magnetic core. The induced magnetic field is used to attract a metal whose mechanics come together to make the machine work.

Complete answer:
Let’s first understand how an electromagnet works. A wire is wrapped around a magnetic core. By the property of moving charges, when current flows through a conductor, it produces a magnetic field. Thus when current flows through a conductor, it generates a magnetic field as long as there is supply of current. When the supply is cut off, the induced magnetic field also diminishes.

The magnetic core is composed of ferromagnetic or ferromagnetic substances in order to maximize the magnitude of induced electromagnetism. Let’s now look at the common uses of electromagnets. Electromagnets are used in electric motors, bells, radios etc.

The motors used in a fan contain a thick sheet of magnetic material like iron, nickel or their alloys, placed in between two poles of the electromagnet. When current is turned on, the sheet under the effects of the magnetic field begins to rotate. This acts as an intermediate in conversion of electric energy to mechanical energy.

(Fig: Representation of an electric motor, Direction of rotation- clockwise)

In electric bells, when we press the button, the circuit is completed, thus ensuring induction of the electromagnetic field as long as we press the switch. Under the effect of this field, the clamper is attracted towards the electromagnet. Its path is blocked by a bell and the clamper hits the bell, whenever the circuit is complete.

In radios, the speakers are electromagnets themselves. These are coils wrapped around tubes placed on the base of the speaker. Whenever a change in magnetic field is countered, they move in certain predetermined ways to produce different types of sound. This happens when the receiver of the radio, accepts radio-waves from the transmitter.

But, in case of heaters, the electric current when moving through the coil produces thermal-effects, that is the effect of current of producing heat when moving through a conductor.

Therefore the correct answer is D, electric-heaters don’t require electromagnets for generating heat, rather the other mentioned appliances require electromagnets.

Note: When a magnetic field is induced in a coil, it continuously changes direction, thus the poles of an electromagnet are always altered, representing something like a wave function. In electric motors, a device called commuter is present which changes the direction of current in order to make the sheet rotate in one direction only. Examples of electromagnetic devices are:- buzzers, bells, tape-recorders, motors, transformers, generators etcetera.