Consider the following four possibilities for two point charges and choose the one(s) that do not change the magnitude of the electrostatic force that each charge exerts on the other:

Question

A. Double the magnitude of each charge and double the separation between them.
B. Double the magnitude of each charge and reduce the separation between them to half of its initial value.
C. Double the magnitude of only one charge and double the separation between the charges.
D. Double the magnitude of only one charge and increase the separation between the charges by a factor of square root(2).

I'm not really sure about this problem. I believe A is correct? I think D might also be correct, but I can't work out the math using theoretical #'s to make sure I'm correct. Someone please help explain this to me.

Answer 1

a,d

(a)k•q1•q2/r² = k•2q1•2q2/(2r)²
(d)k•q1•q2/r² = k•2q1•q2/(√2r)²

Answer 2

The answer is A and D, you are correct.