The correct option is A μ0I4(1R1−1R2)
Magnetic field due to the two straight wire segments at O is zero because point O is lying on the axis of wire. So magnetic field at point O will be produced due to semicircular segments only.
Thus, the magnetic field due to the inner semicircle of radius R1 is given by,
Now using right- hand thumb rule for the direction of magnetic field
⨂ indicates the direction of magnetic field perpendicularly inwards to the plane of paper.
Similarly, the magnetic field due to the outer semicircle of radius R2 is given by,
So, the net magnetic field at point O will be
(considering inward direction to the plane of paper is positive)
Thus, the direction of the resultant field will be perpendicular and into the plane of page.