Question

The distance between two magnetic pole is doubled and the pole strength of each is halved, the force between them will be

• A. Halved
• B. Unchanged
• C. Double
• D. (1/16) times

Answer 1

Answer: (D)

Here $F=\frac{{\mu }_0}{4\pi }\frac{q_m{q}_m}{r^2}$
when pole strength is halved and distance is doubled, the force becomes
$F^{\prime }=\frac{{\mu }_0}{4\pi }\frac{q_m{q}_m/4}{(2r{)}^2}=\frac{F}{16}$