SAT Subject Physics Practice Question 648: Answer and Explanation

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Question: 648

14. A gamma ray is emitted from the nucleus of an unstable atom. What is the result?

A. The number of electrons decreases.
B. The number of electrons increases.
C. The mass of the nucleus increases.
D. The mass of the nucleus decreases.
E. The mass of the nucleus remains the same.

Correct Answer: E


The correct answer is (E). Gamma radiation has no mass. It is emitted from an unstable nucleus, which changes to a lower energy state. There is no mass change involved, so the nucleus remains essentially the same minus the emitted energy.

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