Dear Student ,
An electric bell is made up of a coil of wire wound on an iron piece which acts as an electromagnet, when the electric current is passed through it. An iron strip with a hammer at one end is kept close to the electromagnet. There is a contact screw near the iron strip. When the switch is in the 'ON' position, the current flows through the coil, it becomes an electromagnet. It pulls the iron strip and the hammer at the end of the strip strikes the gong to produce sound. When the electromagnet pulls the iron strip, the circuit breaks and the current stops flowing. The above process is repeated again and again to continue producing sound.
---------------
Screw is a short, slender metal with sharp-pointed pin and slotted head. It is used to join things together.
Regards