Question

Two point charges, initially 2 cm apart, are moved to a distance of 10 cm apart. By what factor does the resulting electric force between them change?

a. 5 b. (1/5) c. (1/25)

Answer 1

The answer is C since: \[F=k\frac{q_1q_2}{r^2}\]The key here is to note that the force is proportional to 1/r^2...and you increased r by a factor of 5 in this question.