Same chapter2 marksDifficulty: Medium
Why does a transformer not work on a direct-current supply?
Electromagnetism
3 marksDifficulty: Medium
Why is soft iron used for the core of an electromagnet and steel for a permanent magnet?
Original Khojo Papers practice question — not from a past board paper.
Answer
Soft iron is magnetised strongly while the current flows but loses almost all its magnetism as soon as the current is switched off, which is exactly what an electromagnet needs. Steel is harder to magnetise but retains its magnetism afterwards, which is what a permanent magnet needs.
No citable source has been recorded for this record. Treat it as practice material, not as fact.
Explanation
The property being used is retentivity, which is low for soft iron and high for steel.
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