The annular disc of copper, with inner radius a and outer radius b is rotating with a uniform angular speed `omega`, in a region where a uniform magnetic field B along the axis of rotation exists. Then, the emf induced between inner side and the outer rim of the disc is-

Options

A. Zero
B. `1/2 B omega a^(2)`
C. `1/2 B omegab^(2)`
D. `1/2 B omega (b^(2)-a^(2))`