Q 12-05-022NEETJEE MainEasy
Materials used for making permanent magnets should have
Answer: (A) high retentivity and high coercivity
Concept. A permanent magnet must keep its magnetisation once the magnetising field is removed and must not lose it easily.
Step 1. Required properties.
- Keeping a large magnetisation at $H = 0$ needs high retentivity.
- Resisting demagnetisation by stray fields needs high coercivity.
Steel and alnico meet both. Electromagnet and transformer cores need the opposite (low coercivity, small hysteresis loss).
Answer. High retentivity and high coercivity (Option A).
Solution by Sreeraj P, M.Sc Physics