Q.

The coercivity of a bar magnet is 120 A/m. It is to be demagnetised by placing it inside a solenoid of length 120 cm and number of turns 72. The current flowing through the solenoid is

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a

0.5A

b

1A

c

2A

d

3A

answer is C.

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Detailed Solution

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In figure, OC represents the coercivity.

Question Image

OC = H = ni 
where n is number of turns per unit length. Here,
n=72120×100=60
and H = 120A/m
i=Hn=12060=2A

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The coercivity of a bar magnet is 120 A/m. It is to be demagnetised by placing it inside a solenoid of length 120 cm and number of turns 72. The current flowing through the solenoid is