A thin metallic disc is rotating with constant angular velocity about a vertical axis that is perpendicular to its plane and passes through its centre. The rotation causes the free electrons in the disc to redistribute. Assume that there is no external electric or magnetic field. Then
(A) a point o the rim of the disc is at a higher potential than the centre
(B) a point on the rim of the disc is at a lower potential than the centre
(C) a point on the rim of the disc is at the same potential as the centre
(D) the potential in the material has an extremum between center and the rim.