SAT Subject Physics Practice Question 99: Answer and Explanation

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Question: 99

9. A particle of charge –0.04 C is projected with speed 2 × 104 m/s into a uniform magnetic field, B, of strength 0.5 T. If the particle’s velocity as it enters the field is perpendicular to B, what is the magnitude of the magnetic force on this particle?

A. 4 N
B. 8 N
C. 40 N
D. 80 N
E. 400 N

Correct Answer: E


Since v is perpendicular to B, the strength of the magnetic force, FB, is just qvB, where q is the magnitude of the charge. In this case, then, we find that

FB = (0.04 C)(2 × 104 m/s)(0.5 T) = 400 N

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