1. The problem statement, all variables and given/known data Two coils have the same number of circular turns and carry the same current. Each rotates in a magnetic field in a setup similar to the square coil in the figure below. Coil 1 has a radius of 4.2 cm and rotates in a 0.19 T field. Coil 2 rotates in a 0.42 T field. Each coil experiences the same maximum torque. What is the radius (in cm) of coil 2? http://www.webassign.net/CJ/21-21.gif 2. Relevant equations Torque= NIABsin(phi) 3. The attempt at a solution I thought that since each coil experienced the same maximum torque and received the same current that I could set their respective NIABsin(phi) equations equal to each other, cancel out current, and solve for the area of the second coil, but the answer that I got was incorrect (8.899 cm). So I know that there has to be another way to solve this question, but I'm at a loss as to how to approach it. Can anyone offer any guidance or insight on what I'm doing wrong?