Please wait for the animation to completely load.
Find the current in the red wire. You can drag the red wire around and read the force/length on it. You can also read the value of the magnetic field at given points in the animation when your mouse is not on a wire (position is given in centimeters, magnetic field strength is given in 10-5 tesla, and force/length is given in newtons/meter). You can also turn the current in the red wire on and off by pushing the buttons. Restart.
Problem authored by Anne J. Cox, Wolfgang Christian and Mario Belloni.