SAT Subject Physics Practice Question 100: Answer and Explanation

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Question: 100

10. A charge of mass m and charge q is moving in a circle of radius r and speed v due to a uniform magnetic field B. If the speed is doubled to 2v, what happens to the period, T ?

A. T increases by a factor of 2
B. T increases by a factor of 4
C. T stays the same
D. T decreases by a factor of 2
E. T decreases by a factor of 4

Correct Answer: C

Explanation:

The period T is the time it takes the charge to complete one revolution: T = Since the magnetic force is providing the centripetal force, Therefore, T = Since T is independent of v, it will remain unchanged.

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