‘Ting-tong’, the most common sound we heard when somebody knocks our door. This sound comes from the instrument located outside door; we called it as electric bell. Electric bell works on principle of magnetic effect of electric current.
Fig. shows the schematic circuit diagram of electric bell. It consists of the following parts.
- E:-Electromagnet, formed by winding copper wire on frame of soft iron core.One end connected to positive terminal of battery, through key.
- H:-Hammer, mostly iron rod with spherical tip.
- S:-Steel rod, acts a spring which pulls back the hammer.
- V:-Battery, (source of electric energy)
- K:-Tap key.
- T:-Screw, connected to negative terminal of battery.
- G:-Gong, which is hollow hemisphere made up of metal which produces sound.
When switch (K) is ON, screw (T) touches the metal strip which completes the circuit and electric current start flowing through the coil of electromagnet, magnetic field is produced and the frame of soft iron gets magnetised. The hammer which is a magnetic material gets attracted towards iron core with certain force hits the gong (bell) and produces a sound. When we release the switch, screw disconnects the circuit and hammer is pulled back to its original position due to the spring action of the steel rod. The process repeats itself and you hear a sound since the hammer keeps hitting the bell, until the switch is released. Now a day we hear some different sounds because instead of gong, door bell has recorded sound mechanism kept near electromagnet such that, on hitting of hammer current flows through it and gets rang.
Q. What is the most important part of electric bell?
Ans: – Electromagnet, formed by winding copper wire on frame of soft iron core.
Q. What is the operating principle of electric bell?
Ans: Electric bell works on principle of magnetic effect of electric current.
Q. How hammer gets back to its original position when we release the switch?
Ans: -When we release the switch, screw disconnects the circuit and hammer is pulled back to its original position due to the spring action of the steel rod.