A metallic rod of length `l` is hinged at the point `M` and is rotating about an axis perpendicular to the plane of paper with a constant angular velocity `omega`. A uniform magnetic field of intensity `B` is acting in the region (as shown in the figure) parallel to the plane of paper. The potential difference between the points `M` and `N`
A. Is always zero
B. Varies between `(1)/(2) Bomegal^(2)` to 0
C. Is always `(1)/(2) B omega,^(2)`
D. Is always `Bomegal^(2)`