SAT Subject Physics Practice Question 214: Answer and Explanation

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Question: 214

60. Four point charges, two positive and two negative, are fixed in position at the corners of a square, as shown below.

Which one of the following arrows best illustrates the total electrostatic force on the charge in the lower right-hand corner of the square?

A.
B.
C.
D.
E. The electric force on this charge is 0.

Correct Answer: A

Explanation:

By the principle of superposition, the total electric force on the charge in the lower right-hand corner is simply the sum of the individual electric forces produced by each of the charges in the other three corners. The first diagram below shows the directions of the individual electric forces that each of the other three charges exerts separately on the lower right-hand charge. The second and third diagrams then show how these three vectors add together to give the net electric force.

Note that F2 and F3 are each larger than F1 since FE = . Therefore, F2 + F<

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