Question

The magnetic moment of a bar magnet of length $20cm$ is $3.6\times {10}^{-6}A{m}^2$. The magnetic length is $90\%$ of its geometric length. The pole strength is:

• A. $2\times {10}^{-5}Am$
• B. $1.8\times {10}^{-4}Am$
• C. $7.2\times {10}^{-8}Am$
• D. $0.55\times {10}^{-4}Am$

Answer 1

The correct option is A $2\times {10}^{-5}Am$

$M_1=3\cdot 6\times {10}^{-6}A{m}^2$
$L_1=20cm$
magnetic length L' $=\frac{20\times 90}{100}cm.$
$M_1=P{L}^{\prime }$
$3\cdot 6\times {10}^{-6}=P\times \frac{20\times 90}{100\times 100}$
$P=2\times {10}^{-5}Am.$