Two long bar magnets are aligned so that north poles face each other. The magnets are separated by 1 cm, and a repulsive force between the north poles is 0.04 N. When the separation is increased to 2 cm the force will be
A) 0.010 N.
B) 0.020 N.
C) 0.025 N.
D) 0.40 N.
E) 0.050 N.

Question

Quizplus · Accepted Answer

The force between two magnetic poles is inversely proportional to the square of the distance between them. Doubling the distance (from 1 cm to 2 cm) decreases the force by a factor of 4 (2^2), so the new force is 0.04 N / 4 = 0.010 N.

Two Long Bar Magnets Are Aligned So That North Poles