EMF induced via change in magnetic flux vs. velocity in magnetic field

1. Oct 1, 2012

I_am_a_person

1. The problem statement, all variables and given/known data
(See attached diagram)--Note this problem was taken from Barron's SAT Physics Practice Test 1 #58
As the loop rotates, the induced voltage will be maximum at...
a) 0 degrees and 90 degrees
b) 0 degrees and 180 degrees
c) 90 degrees and 270 degrees
d) 180 degrees and 270 degrees
e) it will be constant throughout rotation

2. Relevant equations
emf = -Δ∅/Δt
emf = L (v * B)

3. The attempt at a solution
The answer simply states that since the line of wire's direction of velocity is most perpendicular to B (the magnetic field) at 90 and 270 degrees, using emf = L (v * B) (where "*" denotes cross-product), then the emf will be maximized at 90 and 270.

However the answer never says anything about Lenz's law, so how would that play into everything? Wouldn't the change in flux through the loop cause a reverse current (with respect to the current caused by emf = LvB) at some degrees? Or is there a reason why we don't consider Lenz's law here?

Attached Files:

• Barron's Practice Test 1 Problem 58.png
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Last edited: Oct 1, 2012