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

## Homework Statement

(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

emf = -Δ∅/Δt
emf = L (v * B)

## 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?

Last edited: