Question

In two separate experiments, the neutral points due to two small magnets are at a distance of $r$ and $2 r$ in broad side-on position. The ratio of their magnetic moments will be

• A. 4 : 1
• B. 1 : 2
• C. 2 : 1
• D. 1 : 8

Answer 1

Answer: (D)

At broad side-on position, $B=\frac{M}{d^{3}}$
$\therefore \frac{M_{1}}{d_{1}^{3}}=\frac{M_{2}}{d_{2}^{3}}$
or $\frac{M_{1}}{r^{3}}=\frac{M_{2}}{8 r^{3}}$
or $\frac{M_{1}}{M_{2}}=\frac{r^{3}}{8 r^{3}}=\frac{1}{8}$