Conceptual question on induced EMF

[BuBbLeS01]

Homework Statement

A circular loop of wire is rotated at constant angular speed around an axis whose direction can be varied. In a region where a uniform magnetic field points straight down, what must be the orientation of the loop's axis of rotation if the induced emf is to be zero?

Homework Equations

The Attempt at a Solution

I know the answer is vertical but is it vertical because the magnetic field is vertical??

 

[Nabeshin]

Via faradays law of induction, an EMF will be produced when the flux is changing. If you think about this one, it states that the object is rotations, so you have to think of an axis which the flux will be constant even though it rotates about this axis. This corresponds to the axis in the direction of b-field because the angle between the two will always be constant (0 or 180 degrees).