A circular loop of wire is rotated at constant angular speed about 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 a maximum?
A) It must be vertical.
B) It must make an angle of 90° to the direction North.
C) It must make an angle of 45° to the direction North.
D) Any horizontal orientation will do.
E) It must make an angle of 45° to the vertical.

Question

Quizplus · Accepted Answer

For the induced emf to be maximum, the rate of change of the magnetic flux through the loop must be maximized. This occurs when the plane of the loop rotates through the magnetic field lines at the fastest rate, which happens when the axis of rotation is perpendicular to the magnetic field. Since the magnetic field is vertical, any horizontal orientation of the axis of rotation will achieve this, making the rate of change of flux (and thus the induced emf) maximum.

A Circular Loop of Wire Is Rotated at Constant Angular