Figure (a) shows two wires, each carrying a current. Wire 1 consists of a circular arc of radius R = 0.020 m and two radial lengths; it carries current i1 = 1.8 A in the direction indicated. Wire 2 is long and straight; it carries a current i2 that can be varied; and it is at distance R/2 from the center of the arc. The net magnetic field B→ due to the two currents is measured at the center of curvature of the arc. Figure (b) is a plot of the component of B→ in the direction perpendicular to the figure as a function of current i2. The horizontal scale is set by i2s = 2.0 A. What is the angle subtended by the arc?

Figure (a) shows two wires, each carrying a current. Wire 1 consists of a circular arc of radius R = 0.020 m and two radial lengths; it carries current i1 = 1.8 A in the direction indicated. Wire 2 is long and straight; it carries a current i2 that can be varied; and it is at distance R/2 from the center of the arc. The net magnetic field B→ due to the two currents is measured at the center of curvature of the arc. Figure (b) is a plot of the component of B→ in the direction perpendicular to the figure as a function of current i2. The horizontal scale is set by i2s = 2.0 A. What is the angle subtended by the arc?