Physics quiz question: speed of moving rod

Physics 205B Quiz 6, spring semester 2011
Cuesta College, San Luis Obispo, CA

A conducting rod 0.50 m in length moves at a constant speed through a uniform 0.15 T magnetic field. The left end 
of the rod is 0.030 V higher in potential than the right end. The speed of the rod is:
(A) 0.0023 m/s.
(B) 0.40 m/s.
(C) 2.5 m/s.
(D) 10 m/s.

Correct answer (highlight to unhide): (B)

The magnitude of the potential difference between the ends of the rod as it moves through this magnetic field (the "motional emf" ε) is:

ε = v·B·L,

where the speed of the rod would then be:

ε/(B·L) = v = (0.030 V)/((0.15 T)·(0.50)) = 0.40 m/s.

(Response (A) is ε·B·L; response (C) is B·L/ε; response (D) is B/(L·ε).)

Section 30882
Exam code: quiz06eMf0
(A) : 0 students
(B) : 8 students
(C) : 0 students
(D) : 0 students

Success level: 100%
Discrimination index (Aubrecht & Aubrecht, 1983): 0

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