Physics
Describe the construction and working of an electric bell with the help of a neat and labelled diagram.
Answer
Construction :
An electric bell is shown in below figure :
An electric bell consists of the following main parts:
(i) A horse-shoe electromagnet (M) with a soft iron core, wound with coils (CC) in opposite directions.
(ii) A soft iron armature (A) fixed to a metallic spring strip (SS).
(iii) A hammer (H) attached to the armature.
(iv) A gong (G) struck by the hammer.
(v) An adjusting screw (S’) to set the position of the armature.
(vi) A switch or bell-push (K).
(vii) A battery connected across the terminals (T₁ and T₂).
When the switch K is not pressed, the strip SS touches the screw S’, and the armature A remains away from the electromagnet poles.
Working :
When the switch K is pressed, current flows through the coils (CC) and magnetises the electromagnet. This attracts the armature A, causing the hammer H to strike the gong G, producing sound.
As the armature moves, contact between the strip SS and the screw S’ breaks, stopping the current. The electromagnet loses magnetism, and the spring strip pulls the armature back to its original position. Contact is re-established, current flows again, and the cycle repeats.
This make and break action continues rapidly, causing the hammer to strike the gong repeatedly while the switch is pressed.
Related Questions
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State two differences between an electromagnet and a permanent magnet.
Show with the aid of a diagram how a wire is wound on a U-shaped piece of soft iron in order to make it an electromagnet. Complete the circuit diagram and label the poles of the electromagnet.