Question

# The coercivity of a small magnet where the ferromagnet gets demagnetized is 3×103 Am−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:

A
3A
B
6A
C
30 mA
D
60 mA
Solution
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#### Coercivity refers to the intensity of magnetic fields (B) where the magnet gets demagnetisedFor solenoid we have, B=μ0nI (μ0= absolute permeability, n= no. of turns per unit length, B= Magnetic field in solenoid , I= current through each turn)⇒μ0H=μ0nI (H= intensity of magnetic field)⇒I=Hn⇒I=3×103A/m1000.1m=3ASo current needed to be passed through solenoid =3A

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