SAT Subject Physics Practice Question 64: Answer and Explanation
1. If the distance between two positive point charges is tripled, then the strength of the electrostatic repulsion between them will decrease by a factor of
Correct Answer: D
Electrostatic force obeys an inverse-square law: FE ∝ . Therefore, if r increases by a factor of 3, then FE decreases by a factor of 32 = 9.