Question

Label the parts of the given electric bell and explain its working.​
[4 marks]

Answer 1

Let’s label the parts P, Q, R and S.

• P is hammer
  It is a metallic hammer which strikes the gong to produce the sound in an electric bell. [0.5 marks]
• Q is contact screw
  It acts as a switch to break or complete a circuit. [0.5 marks]
• R is gong
  It is the part where the hammer strikes and the sound is produced. As the hammer strikes the gong, the circuit breaks. [0.5 marks]
• S is electromagnet
  The coil wrapped around a soft iron core behaves like a magnet when electric current flows through it. When the electric current is switched off, the coil generally loses its magnetism. These are called electromagnets. [0.5 marks]
  
  

Working:

• The switch is pressed and current flows through the circuit.
• The electromagnet is powered and generates a magnetic effect that attracts the iron strip towards it.
• The striker strikes the gong (bell).
• When the striking arm strikes the gong, the contact is broken and current stops flowing through the circuit.
• This causes the electromagnet to lose its magnetic field.
• The connected spring arm returns the striker to its original rest position.
• The contact is restored and current flows through the circuit (provided the main switch is still pressed).
• The process is repeated from the beginning.

[2 marks]