A current loop ABCD is held fixed on the place of the paper as shown in Fig. 45. The arcs BC (radius = b) and DA (radius = a) of the loop are joined by two straight wires AB and CD. A steady current I is flowing in the loop. Angle made by AB and CD at the origin O is 30°. Another straight thin wire with steady current I, flowing out of the plane of the paper is kept at the origin.
The magnitude of the magnetic field B. due to loop ABCD at the origin (O) is