A wire carrying current I has the shape as shown in adjoining figure. Linear parts of the wire are very long and parallel to X -axis while semicircular portion of radius R is lying in Y-Z plane. Magnetic field at point O is

Given situation is shown in the figure. Parallel wires 1 and 3 are semi-infinite, so magnetic field at O due to themB→1=B→3=-μ0I4πRk^Magnetic field at O due to semi-circular arc in Y Z -plane is given byB→2=-μ0I4Ri^ Net magnetic field at point O is given by B→=B→1+B→2+B→3=-μ0I4πRk^-μ0I4Ri^-μ0I4πRk^=-μ0I4πR(πi^+2k^)