Two point charges are 12 cm apart.They are moved to a new separation of 3 cm.By what factor does the resulting mutual force between them change?
A)1/4
B)4
C)1/16
D)16
E)4.5

Question

Two point charges are 12 cm apart.They are moved to a new separation of 3 cm.By what factor does the resulting mutual force between them change?
A)1/4
B)4
C)1/16
D)16
E)​4.5

Quizplus · Accepted Answer

The force between two charges is given by Coulomb's law: F = k(q1q2)/r^2. 
When the separation distance is decreased from 12 cm to 3 cm, the denominator of the formula decreases by a factor of (12/3)^2 = 16. 
Thus, the force between the charges increases by a factor of 16. 
Therefore, the correct answer is D) 16.

Two Point Charges Are 12 Cm Apart