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Question

A bar magnet has a coercivity of 4×103Am1. It is placed inside a solenoid of length 12 cm having 60 turns in order to demagnetize it, the amount of current that should be passed through the solenoid is:
  1. 16 A
  2. 8A
  3. 4 A
  4. 2 A

A
2 A
B
8A
C
16 A
D
4 A
Solution
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Given: H=4×103 Am1

L=12 cm

N=60

Bar magnet requires a magnetic intensity (H=4×103 Am1) to become demagnetized.

Let n be the number of turns per unit length.

n=NL=600.12=500 turns/metre

Now, H=nI

I=Hn=4×103500=8 A

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