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Magnetism And Matter — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsMagnetism And Matter1 Mark
Question
The coercive force for a certain permanent magnet is $4.0 × 10^4\ A/m.$Thia magnet is placed inside a long solenoid of 40 turns/cm and a current is passed in the solenoid to demagnetise it completely. Find the current.
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Answer

$\text{B}=\mu_0\text{ni},\ \text{H}=\frac{\text{B}}{\mu_0}$
Given n = 40 turns/cm = 4000 turns/m
$⇒ H = ni$
$H = 4 × 10^4\ A/m$
$\Rightarrow\text{i}=\frac{\text{H}}{\text{n}}=\frac{4\times10^4}{4000}=10\text{A}.$

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