SAT Subject Physics Practice Question 76: Answer and Explanation

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Question: 76


Which expresses the value of the electric potential at the center of the square?

A. 0

Correct Answer: E


3 E The electric potential due to any one of the charges is , where r = , since the distance from the charge to the center has that value. (To show this, draw a right triangle, the hypotenuse of which is the line from the center of the square to a charge. You’ll have a base and a height of length s/2.) That is, the potential due to one charge is . The potential due to four charges is just four times that potential, since electric potentials are scalars and just add together if they are all positive, so the total is .

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