# Application of Electromagnet

Card 1: Electric Bell

## Electric Bell

When the switch is on, the circuit is completed and current flows. The electromagnet becomes magnetised and hence attracts the soft-iron armature and at the same time pull the hammer to strike the gong.

As soon as the hammer moves towards the gong, the circuit is broken. The current stops flowing and the electromagnet loses its magnetism. This causes the spring to pull back the armature and reconnect the circuit again.

When the circuit is connected, the electromagnet regain its magnetism and pull the armature and hence the hammer to strike the gong again. This cycle repeats and the bell rings continuously.

Card 2: Electromagnetic Relay

## Electromagnetic Relay

A relay is an electrical switch that opens and closes under the control of another electrical circuit.

A relay has at least two circuits. One circuit can be used to control another circuit. The 1st circuit (input circuit) supplies current to the electromagnet. The electromagnet is magnetised and attracts one end of the iron armature.

The armature is then closes the contacts (2nd switch) and allows current flows in the second circuit. When the 1st switch is open again, the current to the electromagnet is cut, the electromagnet loses its magnetism and the 2nd switch is opened. Thus current stop to flow in the 2nd circuit.

Card 3: Circuit Breaker

## Circuit Breaker

The figure shows the structure of a circuit breaker. A circuit breaker is an automatic switch that cut off current in a circuit when the current become too large.

When the current in a circuit increases, the strength of the electromagnet will increase in accordance; this will pull the soft iron armature towards the electromagnet.

As a result, the spring pulls apart the contact and disconnects the circuit immediately, and the current stop to flow.

We can reconnect the circuit by using the reset button. The reset button can be pushed to bring the contact back to its original position to reconnect the circuit.

Card 4: Telephone Earpiece

## Telephone Earpiece

An electromagnet is used in the earpiece of a telephone. The figure shows the simple structure of a telephone earpiece.

When you speak to a friend through the telephone, your sound will be converted into electric current by the mouthpiece of the telephone. The current produced is a varying current and the frequency of the current will be the same as the frequency of your sound. The current will be sent to the earpiece of the telephone of your friend.

When the current passes through the solenoid, the iron core is magnetised. The strength of the magnetic field changes according to the varying current. When the current is high, the magnetic field will become stronger and when the current is low, the magnetic field become weaker.

The soft-iron diaphragm is pulled by the electromagnet and vibrates at the frequency of the varying current. The air around the diaphragm is stretched and compressed and produces sound wave. The frequency of the sound produced in the telephone earpiece will be the same as your sound.

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