a wire is formed in a complete loop a shown below. the two circular arcs span 2/3 of a circle and are concentric; that is, they share the same center. the inner arc has a radius of 3a/5, and the outer arc has a radius of 4a/3. any segments connecting the arcs travel radially. what are the magnitude and direction of the magnetic field at the center of the loop if a current i travels as indicated? use biot-savart law to solve this and include arguments about why segments do not contribute to the magnetic field