Q149 / 160 · TS EAMCET 2023 (12 May Shift 1) · Physics

A bar magnet has coercivity $4 \times 10^3 \mathrm{Am}^{-1}$. It is placed inside a solenoid of $12 \mathrm{~cm}$ length and 60 turns. The current that should be passed through the solenoid to demagnetise the bar magnet is

  • A
    $2A$
  • B
    $4A$
  • C
    $6A$
  • Correct answer
    D
    $8A$

Solution

Coercivity of bar magnet, $\mathrm{H}=4 \times 10^3 \mathrm{~A} / \mathrm{m}$ Length of solenoid, $\mathrm{L}=12 \mathrm{~cm}=0.12$ Number of turns, $\mathrm{N}=60$ turns $\mathrm{n}=\frac{\mathrm{N}}{\mathrm{L}}=\frac{60}{0.12}=500 \mathrm{turn} / \mathrm{m}$ Current, $i=\frac{H}{n}=\frac{4 \times 10^3}{500}=8 \mathrm{~A}$

Hence, the correct answer is option: 'D'.

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