Electric bell is a type of bell operated by an electric current. There are two types of electric bells. One type rings continuously when the switch that controls it is on. This type of bell is commonly used in schools and factories. The other kind, the door chime, rings only once or twice when the switch is turned on—that is, when the doorbell button is pushed.
The parts of a continuously ringing bell include the switch; an electromagnet, a device that acts as a magnet when a current runs through it; and an armature, a movable metal part. A clapper is attached to the end of the armature. Also attached to the armature is a spring that rests against a screw. Wiring runs from the source of electric current to the switch and from the switch to the electromagnet. Another wire runs from the screw back to the source of the electric current. Together, the parts of the bell form an electric circuit.
When the switch is turned on, the current flows through the electromagnet, and the electromagnet attracts the armature. The movement of the armature causes the clapper to strike the bell and the spring to move off the screw. When the spring moves off the screw, the circuit is broken and the current stops flowing. Then, the armature falls away from the electromagnet. When the armature returns to its original position, the spring comes in contact with the screw again and reestablishes the flow of electric current. The process repeats and the electric bell keeps ringing as long as the operating switch is on.
A door chime does not have the spring and screw. Thus, the armature and clapper move only once each time the control switch is operated, and the bell sounds only once. If a second bell is set up for the clapper to strike when it falls away from the first bell, two sounds can be produced for each switch operation.
