of Electric Current
A solenoid is a cylindrical coil of wire that behaves like a bar magnet when current flows through it.
If we insert a piece of iron in a coil carrying current, then iron gets strongly magnetised.
This principle is used to make strong electromagnets.
The iron nail in the experiment behaves like a magnet only as long as the current is flowing in the circuit.
The pins cling to the nail when the switch is ON while they drop as soon as the switch disconnects, the electric circuit.
An electric bell is the most common application of electromagnets.
It consists of an electromagnet, a springy iron strip, a hammer, a gong, a switch and connecting wires.
When you press the switch of the call bell at your door, the current passes through the circuit.
The electromagnet pulls the springy iron strip S which forms one terminal of the switch T.
As the strip moves towards the electromagnet, its contact with the switch is lost. This breaks the circuit.
As a result, the electromagnet stops attracting the strip. The strip goes back to its original position (due to spring) and it's contact with the switch is re-established.
This backward and forward movement of the iron strip takes place many a times in a second and produces sound.
The loudness of the sound may be enhanced with the help of a hammer attached to the strip S which in turn strikes the gong G.
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