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A solenoid is also called an 'electromagnet'. Why does inserting an iron core greatly increase its magnetic field?
AIron core conducts current better
BIron has high magnetic permeability μ_r >> 1 (ferromagnetic): aligned domains add to the field, multiplying B by hundreds or thousands
CIron heats up and emits magnetism
DAir resistance is removed
Answer & Solution
Correct answer: B. Iron has high magnetic permeability μ_r >> 1 (ferromagnetic): aligned domains add to the field, multiplying B by hundreds or thousands
With ferromagnetic core, B = μ_r μ₀ n I where μ_r is the relative permeability. For iron, μ_r ≈ 1000 to 5000. So the field increases dramatically. This is why electromagnets used in industry have iron cores.
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