SAT Subject Physics Practice Question 97: Answer and Explanation

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Question: 97

7. Due to the magnetic force, a positively charged particle undergoes uniform circular motion in a uniform magnetic field. Which of the following changes could cause the radius of the circular path to decrease?

A. Increase the mass of the particle
B. Increase the speed of the particle
C. Decrease the charge of the particle
D. Decrease the strength of the magnetic field
E. None of the above

Correct Answer: E

Explanation:

The magnetic force provides the centripetal force on the charged particle. It follows that

Increasing m or v, or decreasing q or B, would make r larger, not smaller. Therefore, the answer must be E.

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