The soft-iron is a suitable material for making an electromagnet. This is because soft-iron has

Solution

Physics sir · 3 steps

An electromagnet must switch on strongly and switch off cleanly; pick the property that does each job.

1. Two jobs. With current on, the core must become a strong magnet. With current off, the core must lose that magnetism almost at once.

   Property	What it tells you	Electromagnet needs
   Permeability μ	How easily the core magnetises for a given current	High, so a small current gives a strong field
   Retentivity	Magnetism left in the core after the current is removed	Low, so the magnet switches off
   Coercivity	Reverse field needed to wipe out the leftover magnetism	Low, so any leftover magnetism is easy to remove

2. Match options. Only one option pairs high permeability with low retentivity. Option (a) and option (d) keep the magnetism after switch-off, and option (b) gives a weak magnet.
3. So. Soft iron suits an electromagnet because it has high permeability and low retentivity, which is option (c).

The idea to keep. Electromagnet core: easy to magnetise and easy to demagnetise, so high permeability and low retentivity. Permanent magnet: the opposite, with high retentivity and high coercivity.

Answer from the NTA final answer key. Solution by PrepWiser.