SAT Subject Physics Practice Question 241: Answer and Explanation

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Question: 241

12.

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).

If a negative charge, –q, were moved along the x axis from x = –a to x = a, which graph best depicts the magnitude of the electric force it would feel during this motion?

A.
B.
C.
D.
E.

Correct Answer: B

Explanation:

If a charge –q is at a location where the electric field is E, then the electric force on the charge is F = (–q)E, and the magnitude of this force is qE. Since the magnitude of the electric force, F, is proportional to the electric field strength, the graph of F should have the same shape as the graph of E.

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