Calculate the magnetic field at distance `y` from the centre of the axis of a disc of radius `r` and unifrom surface charge density `sigma`, If the disc spins with angular velocity `omega` ?

Options

A. `(mu_(0)sigma omega)/(2)((R^(2)+y^(2))/(sqrt(R^(2)+y^(2))))`
B. `(mu_(0)sigma omega)/(2) ((R^(2)+y^(2))/(sqrt(R^(2)+y^(2)))-2y)`
C. `(2 mu_(0) sigma omega)/(3) ((R^(2)+y^(2))/(sqrt(R^(2)+y^(2)))-2y)`
D. `(mu_(0)sigma omega)/(3)((R^(2)-2y^(2))/(sqrt(R^(2)-y^(2)))+2y)`

Answer

B