Question

The magnetic potential due to a magnetic dipole at a point on its axis distant $40\, cm$ from its centre is found to be $2.4 \times 10^{-5} JA ^{-1} m ^{-1}$. The magnetic moment of the dipole will be

• A. $28.6\, Am ^{2}$
• B. $32.2\, Am ^{2}$
• C. $38.4\, Am ^{2}$
• D. None of these

Answer 1

Answer: (C)

Here, $r=40\, cm =0.4\, m$
$\theta=0^{\circ}$ (an axial line)
$V=2.4 \times 10^{-5} J / A - m ; M =?$
As, $V =\frac{\mu_{0}}{4 \pi} \frac{M \cos \theta}{r^{2}}$
$\Rightarrow 2.4 \times 10^{-5} =10^{-7} \frac{M \times 1}{(0.4)^{2}}$
or $M =38.4\, Am ^{2}$