SAT Subject Physics Practice Question 655: Answer and Explanation

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Question: 655

6. During an electrostatics experiment a student touches an electroscope with a negatively charged rod, and the leaves of the electroscope separate. What will be the result when a second positively charged rod is brought near, but does not touch, the electroscope?

A. The leaves will begin to flutter.
B. The leaves will separate further.
C. The leaves will move closer together.
D. The leaves will be unaffected.
E. None of the above will happen.

Correct Answer: C


The correct answer is (C). The positively charged rod attracts the excess electrons that were deposited by the negatively charged rod. The movement of the electrons toward the positive rod reduces the repulsive force applied to the leaves, and the leaves are able to move closer to one another.

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