Question
The coercive force for a certain permanent magnet is $4.0 \times 10^4A/m$. 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.
✓
Answer
$\text{B}=\mu_0\text{ni},\ \text{H}=\frac{\text{B}}{\mu_0}$
Given $n = 40 \ turns/cm = 4000 \ turns/m$
$\Rightarrow H = ni$
$H = 4 \times 10^4A/m$
$\Rightarrow\text{i}=\frac{\text{H}}{\text{n}}=\frac{4\times10^4}{4000}=10\text{A}.$
Given $n = 40 \ turns/cm = 4000 \ turns/m$
$\Rightarrow H = ni$
$H = 4 \times 10^4A/m$
$\Rightarrow\text{i}=\frac{\text{H}}{\text{n}}=\frac{4\times10^4}{4000}=10\text{A}.$
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