Introduction: An electric bell is a very common instrument. The moment you have a visitor generally the first thing you hear is the calling bell or when you visit somebody else's place, we are used to pressing a switch and listening to noise. It could be the sound of a bird, or a ring etc. The ubiquitous calling bells. This is an electric bell working on electricity. So how does this work? Before you get into the working of an electric bell, let us just briefly touch upon what is called electromagnetism. When current flows through a coil, we are aware that it creates a magnetic field. When you take an insulated current carrying wire and coil it around a metal, what you get is an electromagnet. The magnet's power can be increased by increasing the number of turns that you coil around the metal and it can also be increased when the flow of current is increased through the wire. Now when you stop the current flowing through the coil, what you essentially do is that the property of electromagnetism of the metal has been suspended. It is the current that flows, which makes it an electromagnet.
With the basics of electromagnet touched upon, we can now get into understanding how an electric bell works.
Consider, now the switch to be in OFF position. As we can see, there is a coil of wire wound around a U shaped metal which resembles a horseshoe magnet. You also see a spring-loaded arm with a soft iron armature kept close to the electromagnet let's call this a clapper. The other end of the arm has a hammer attached to it. There is a small metal gong kept near the hammer. A spring-loaded arm (shown as spring in the drawing) is connected close to the clapper from the battery which is the power source. When the circuit is switched on, the current flows through the spring onto the clapper and through the coil into the horseshoe-shaped magnet and the circuit gets completed with the flow of current. When the current begins to flow through the coil it becomes an electromagnet. The electromagnet will now pull the clapper towards itself. When this happens, the hammer strikes the gong and produces a sound. When the clapper is pulled inwards, the contact between the spring and the clapper is broken, resulting in the circuit getting disconnected. When this happens, the current flow stops, and the coil ceases to be an electromagnet. Immediately the clapper is released to its original position and comes into contact with the spring. The moment it comes into contact with the spring, the circuit is closed, and the coil becomes an electromagnet pulling the clapper again inside. This cycle repeats as long as the switch is pressed, and the bell continues to ring. This cycle happens at a very high speed which makes you hear the ring sound in a calling bell.
Hence, it is the property of electromagnetism that makes an electric bell work by moving the clapper in and out as and when the current flows through the coil.