Question

The magnetic induction of a distance d from the magnetic pole of unknown strength m is B. If an identical pole is now placed at a distance of 2d from the first pole, the force between the two poles is:

• A. mB
• B. $\frac{mB}{2}$
• C. $\frac{mB}{4}$
• D. 2mB

Answer 1

Answer: (C)

$B=\frac{{\mu }_0}{4\pi }\frac{m}{d^2}$ $\therefore$ $F=mB$ $=m\times \frac{{\mu }_0}{4\pi }\frac{m}{{(2d)}^2}$ $=\frac{m}{4}B$