SAT Subject Physics Practice Question 240: Answer and Explanation

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Question: 240

11.

An electric dipole, a pair of equal but opposite charges. Two isolated point charges are fixed in the positions shown on the y axis; the positive charge is located at the point (0, b) and the negative charge is located at the point (0, –b).

Which graph best illustrates the electric potential along the x axis, from x = –a to x = a?

A.
B.
C.
D.
E.

Correct Answer: A

Explanation:

Every point on the x axis is equidistant from the source charges. For any given point, P, on the x axis, let R denote its distance from the +Q charge and from the –Q charge. Then the potential at P is k(+Q)/R + k(−Q)/R = 0. Therefore, the potential is zero everywhere along the x-axis, so graph A is the answer.

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