Magnetic Properties of Matter

JEE Main level, single correct, medium

54 of 57

Question 54 of 57

The coercivity of a small magnet, where the ferromagnet gets demagnetised is 3×103A/m3\times {10}^{3}A/m. The current required to be passed in a solenoid of length 10cm10cm and number of turns 100100, so that the magnet gets demagnetised when inside the solenoid is

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Answer: (C) 3 A

For solenoid, the magnetic field needed to be magnetised the magnet.
B=μ0nIB={\mu }_{0}nI
where, n=100,l=10cm=10100m=0.1mn=100,l=10cm=\dfrac{10}{100}m=0.1m
⇒3×103=1000.1×I\Rightarrow 3\times {10}^{3}=\dfrac{100}{0.1}\times I
⇒I=3A\Rightarrow I=3A

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