SAT Subject Physics Practice Question 64: Answer and Explanation

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Question: 64

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

A. 3
B. 6
C. 8
D. 9
E. 12

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.

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