Which of the following statements is the correct reason for using soft iron in making the armature or an electric bell?

Analyze the question: You are asked why soft iron is used for the armature of an electric bell.

Concept: In an electric bell, current flows through an electromagnet and magnetizes the core. The core attracts the armature, and the hammer strikes the gong. This action breaks the circuit at the contact point, so the current stops. The armature must then spring back quickly so the circuit is remade and the cycle repeats.

For that to work, the iron must:

• be magnetized easily when current flows, and
• lose its magnetism quickly when the current stops.

Soft iron has both properties. It is a soft magnetic material with low retentivity and low coercivity. Steel, by contrast, is hard magnetically. It keeps its magnetism, which is why it is used for permanent magnets.

Checking the options:

• A. Diamagnetic: wrong. Diamagnetic materials are weakly repelled by magnets, but soft iron is ferromagnetic.
• B. Loses its magnetism readily: correct. This lets the armature release and the bell ring continuously.
• C. Not easily magnetized: wrong. Soft iron is magnetized very easily.
• D. Retains its magnetism for a long time: wrong. If it did, the armature would stay stuck to the electromagnet and the bell would stop ringing after one strike.

Answer: B

Tip: Remember "Soft iron = Switch-off magnet" (temporary magnets such as electromagnets, relays, bells). "Steel = Stays magnetized" (permanent magnets).