Physics quiz question: motional emf

Physics 205B Quiz 6, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 20.1

A conducting rod 0.50 m in length moves at a constant speed through a uniform magnetic field. A longer rod 1.0 m in length moving with the same speed in the same direction in this magnetic field would have a potential difference __________ the 0.50 m long rod.
(A) less than.
(B) the same as.
(C) more than.
(D) (Not enough information is given.)

Correct answer: (C)

The motional emf in a rod of length L, moving through a perpendicular, uniform magnetic field B is given by:

emf = v*B*L.

So a longer rod would experience a proportionally greater motional emf.

Student responses
Section 70856
(A) : 0 students
(B) : 2 students
(C) : 9 students
(D) : 0 students

Success level: 81%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.08