Question

A bar magnet of length $3cm$ has points $A$ and $B$ along its axis at distances of $24cm$ and $48cm$ on the opposite sides. Ratio of magnetic fields at these points will be

• A. $8$
• B. $\frac{1}{2\sqrt{2}}$
• C. $3$
• D. $4$

Answer 1

The correct option is A $8$

For a short magnet at a point along its axial line, magnetic field is given by
$B=\frac{{\mu }_0}{4\pi }.\frac{2M}{r^3}$
$\Rightarrow \frac{B_1}{B_2}={\left(\frac{r_2}{r_1}\right)}^3={\left(\frac{48}{24}\right)}^3=\frac{8}{1}=8$