SAT Subject Physics Practice Question 72: Answer and Explanation

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Question: 72


The figure above shows two point charges, +Q and +Q. If the right-hand charge were absent, the electric field at Point P due to +Q would have a strength of E. With the right-hand charge in place, what is the strength of the total electric field at P, which lies at the midpoint of the line segment joining the charges?

A. 0
D. 2E
E. 4E

Correct Answer: A


The individual electric field vectors at P due to the two source charges have the same magnitude and point in opposite directions. Therefore, the net electric field at point P will be zero.

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