Question

A bar magnet has length $3cm$, cross-sectional area $2c{m}^2$ and magnetic moment $3A{m}^2$. The intensity of magnetisation of bar magnet is

• A. $2\times {10}^{5}A/m$
• B. $3\times {10}^{5}A/m$
• C. $4\times {10}^{5}A/m$
• D. $5\times {10}^{5}A/m$

Answer 1

The correct option is D $5\times {10}^{5}A/m$

Length of the bar magnet $L=3cm=3\times {10}^{-2}m$

Area of bar magnet $A=2c{m}^2=2\times {10}^{-4}{m}^2$

Thus volume of bar magnet $V=AL$

$\therefore$ $V=3\times {10}^{-2}\times 3\times {10}^{-4}=6\times {10}^{-6}{m}^3$

Magnetic moment $\mu =3A{m}^2$

Thus intensity of magnetisation $I=\frac{\mu }{V}$

$\therefore$ $I=\frac{3}{6\times {10}^{-6}}=5\times {10}^{5}A/m$