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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 inside the solenoid, is -

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

Correct answer: 3 A

Solution

The correct option is right because the current required to demagnetize the small magnet can be calculated using the formula for the magnetic field inside a solenoid, which is proportional to the product of the current and the number of turns per unit length. Given the coercivity and the dimensions of the solenoid, a current of 3 A is necessary to achieve the required magnetic field to demagnetize the magnet.

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