A metal rod of length L in a region of space where a constant magnetic field points into the page rotates clockwise about an axis through its center at constant angular velocity ω. While it rotates, the point(s) at lowest potential is(are)
A)A.
B)B.
C)C.
D)D.
E)A and E.

Question

A metal rod of length L in a region of space where a constant magnetic field points into the page rotates clockwise about an axis through its center at constant angular velocity ω. While it rotates, the point(s) at lowest potential is(are) 
A)A. 
B)B. 
C)C. 
D)D. 
E)A and E.

Quizplus · Accepted Answer

The point at the center of the rod (point C) is at the lowest potential because it does not move with respect to the magnetic field. The other points on the rod experience a changing magnetic flux as they rotate, which induces an emf and leads to a potential difference along the rod. This potential difference causes an electric current to flow through the rod, which in turn generates a magnetic field that opposes the external magnetic field. This results in a magnetic force that pushes the charged particles (i.e. electrons) in the rod towards the higher potential end, which is at the outer edges of the rod (points A and D). Therefore, the points at the end of the rod (A and D) have the highest potential, while the point at the center of the rod (C) has the lowest potential.

A Metal Rod of Length L in a Region of Space