Question

A short bar magnet is placed with its north pole pointing south. The neutral point is $10cm$ away from the centre of the magnet. If $H=0.4$ Gauss, calculate magnetic moment of the magnet.

• A. $5\times {10}^{-6}A{m}^2$
• B. $1A{m}^2$
• C. $0.1A{m}^2$
• D. $0.2A{m}^2$

Answer 1

The correct option is A $5\times {10}^{-6}A{m}^2$

Magnetic field due to the bar magnet

$H=m4d^2$

where $d$ is the point at which net magnetic field is zero$.$ $($due to earth and the bar magnet$)$

$d=10cm=0.1mH=0.4gauss=0.4\times {10}^{-4T}$ on substituting

$m=5\times {10}^{-6}A{m}^2$

Hence,

option $\left(A\right)$ is correct answer.