Question

A short bar magnet has a length $2l$ and a magnetic moment $10A{m}^2$. Find the magnetic field at a distance of $z=0.1m$ from its centre on the axial line. Here, $l$ is negligible as compared to $z$.

• A. $2\times {10}^{-3}T$
• B. $3\times {10}^{-3}T$
• C. $1\times {10}^{-3}T$
• D. $4\times {10}^{-3}T$

Answer 1

The correct option is A $2\times {10}^{-3}T$

On axial position
$B_a=\frac{{\mu }_0}{4\pi }\frac{2Mr}{(r^2-l^2{)}^2}$; if $l<<r$, then $B_a=\frac{{\mu }_0}{4\pi }\frac{2M}{r^3}$
$B_a=\frac{{10}^{-7}\times 2\times 10}{(0.1{)}^3}=2\times {10}^{-3}T[\because z=r]$.