The current-carrying wire loop in the figure on the left lies all in one plane and consists of a semicircle of radius 20 cm, a smaller semicircle with the same center, and two radial lengths.
The smaller semicircle is rotated out of that plane by angle θ, until it is perpendicular to the plane.
The figure on the right gives the magnitude of the net magnetic field at the center of curvature versus angle θ. The vertical scale is set by Ba = 26.076 μT and Bb = 35.414 μT. What is the radius of the smaller semicircle?