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The coercivity of a small magnet where the ferromagnet gets demagnetized is 3 × 10³ A m⁻¹. The current required to be passed in a solenoid of length 10 cm and number of turns 100, so that the magnet gets demagnetized when inside the solenoid, is:

1. 30 mA
2. 60 mA
3. 3 A
4. 6 A

Correct answer: 3 A

Solution

Demagnetizing field H = (N/L)*I, so I = H*L/N = (3e3 * 0.10)/100 = 3 A.

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