Question

The magnetic field at a point $x$ on the axis of a small bar magnet is equal to the field at a point $y$ on the equator of the same magnet. The ratio of the distances of $x$ and $y$ from the centre of the magnet is

• A. $2^{-3}$
• B. $2^{-1 / 3}$
• C. $2^{3}$
• D. $2^{1 / 3}$

Answer 1

Answer: (D)

$B_{1}=\frac{2 M}{x^{3}}$ and $B_{2}=\frac{M}{y^{3}}$
As $B_{1}=B_{2}$
Hence $\frac{2 M}{x^{3}}=\frac{M}{y^{3}}$
or $\frac{x^{3}}{y^{3}}=2$ or $\frac{x}{y}=2^{1 / 3}$