Figure shows three cases: in all case the circular part has radius r and straight ones are infinitely long. For the same current the ratio of field B at centre P in the three case `B_1:B_2:B_3` is

Options

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

Answer

A