A semi-circular loop consisting of one turn of wire is placed in the x-y plane. A constant magnetic field of magnitude B = 2.7 T points along the negative z-axis (into the page), and a current I = 0.7 A flows counter-clockwise as viewed from the positive z-axis. Find the magnitude of the net magnetic force on the circular section of the loop. a 1=0.7 A A 3.78 N B 4.78 N C 3.87 N D 3.90 N d=2m