A bar magnet has coercivity 4×103Am−1. It is placed in a solenoid having 40 turns per cm and is 1.2m long. The current carried by the solenoid to demagnetize the bar magnet is :
6A
8A
5.78A
none of these
A
none of these
B
8A
C
5.78A
D
6A
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Solution
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H=4∗103A/m
B=H∗l=4∗103A/m∗1.2=48∗102A
μ0=4π∗10−7Tm/a
48∗102=μoNI=4π∗10−7∗40∗I
I=48∗1024π∗10−7∗40=0.095∗109A
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