Question

The magnetic induction field strength at a distance of $0.3\text{m}$ on the axial line of a short bar magnet of moment $3.6{\text{Am}}^2$ is

• A. $2.6\times {10}^{-5}\text{T}$
• B. $9\times {10}^{-5}\text{T}$
• C. $9\times {10}^{-4}\text{T}$
• D. $4.5\times {10}^{-4}\text{T}$

Answer 1

The correct option is A $2.6\times {10}^{-5}\text{T}$

Magnetic induction along the axis of a short bar magnet is,

$B_{ax}$= $\frac{{\mu }_0}{4\pi }$ $\frac{2M}{d^3}$

$={10}^{-7}\times \frac{2\times 3.6}{(3\times {10}^{-1}{)}^3}$

$=\frac{2\times 3.6}{27}\times {10}^{-4}$= $\frac{2\times 4}{3}\times {10}^{-5}$

$=2.6\times {10}^{-5}\text{T}$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(A\right)$ is the correct answer.