Why They Buzz or Ring—Electromagnetism
If we were to look at an electric bell with the cover off, we'd find that it would be very much like Figure 1.
A push on the button, which is just a switch that is normally held "open" or off by means of a spring, sends the current from the battery or transformer through the circuit.
Figure 1
You will see that the current passes first through two small coils of wire, and each coil has at its center a piece of soft iron called the core. When the current is on, the core becomes magnetized and attracts another piece of iron called the armature with its clapper attached.
This action rings the bell, but it also breaks the current by pulling the spring away from the screw on its return to the power supply.
With the power off, the electromagnet lets the spring return the armature to its normal position, contact is made again, and the cycle starts all over again—just as long as you continue to push on the button.
Buzzers work exactly the same way, except that they do not have a bell and depend instead on the vibration of the armature for a noise that's not as loud or as musical.
Gongs or chimes, that strike only once when the button is pushed, are made by connecting the armature with the screw by means of a flexible wire.