申論題

14. The first figure shows a closed loop with current i. The loop consists of a half-circle of radius r and a half circle of radius R = 2r. The second figure shows the same half-circles but the small one has been flipped over. The net magnetic field at the common center of the circular sections is B₁ for the first figure and B2 for the second figure. What is the magnitude of the ratio B₂ / B₁?