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Find the current carried by each of the four wires in the animation. Each wire carries current either into or out of the computer screen (position is given in millimeters and the magnetic field strength is in given in millitesla, 10^-3 T, so the integral is given in mT·mm = 10^-6 T·m). You can turn the integral on, and the cursor will change to a pencil and draw the path as it calculates the integral of the magnetic field in the direction of the path you take (path integral of B · dl.) You can re-zero the integral at any point or turn the integral off and move the cursor to another spot. Restart.

Problem authored by Anne J. Cox.
Script authored by Mario Belloni and Wolfgang Christian and modified by Anne J. Cox.