Current I is flowing in a conductor shaped as shown in the figure . The radius of the curved part is r and the length of straight portion is very large . The value of the magnetic field at the centre O will be

Options

A. `(mu_0I)/(4pi r)(pi/2-1)`
B. `(mu_0I)/(4pi r)(pi/2+1)`
C. `(mu_0I)/(4pi r)((3pi)/2-1)`
D. `(mu_0I)/(4pi r)((3pi)/2+1)`

Answer

D