One student has to make an electromagnet using a coil of copper wire. He needs a ferromagnetic material to make its core. This core material should have
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → High permeability, low retentivity
An electromagnet must become a strong magnet while the current flows and must lose its magnetism when the current is switched off.
A high permeability core gives a strong field for a small current. A low retentivity core keeps very little magnetism once the current stops. Soft iron has both properties.
Option (1) Low permeability, low retentivity — Incorrect. Low permeability gives a weak magnet for the given current.
Option (2) High permeability, high retentivity — Incorrect. High retentivity would leave the core magnetised after the current is switched off; this suits a permanent magnet.
Option (3) Low permeability, high retentivity — Incorrect. Both properties are the wrong way round for an electromagnet.
Option (4) High permeability, low retentivity — Correct. The core magnetises strongly and loses its magnetism when the current stops.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Permanent Magnets and Electromagnets – “… Core of electromagnets are made of ferromagnetic materials which have high permeability and low retentivity. Soft iron is a suitable material for electromagnets. … When we switch off the solenoid current, the magnetism is effectively switched off since the soft iron core has a low retentivity.”