You know that Wires 1 and 2 are a distance, d = 0.81 m, apart and that they carry the same current, I = 18.7 A, in opposite directions. You also know that Wires 2 and 3 are a distance, x = 2.43 m, apart. What you don't know, but really need to find out, is... "How much current flows through Wire 3 -- and which way?" You would just measure the current, if your ammeter wasn't broken. Then you remembered the magnetometer that the Tooth Fairy left under your pillow last year, and realized that you could deduce the current in Wire 3 from the measured magnetic field strength! out down wire 1 wire 2 wire

You know that Wires 1 and 2 are a distance, d = 0.81 m, apart and that they carry the same current, I = 18.7 A, in opposite directions. You also know that Wires 2 and 3 are a distance, x = 2.43 m, apart. What you don't know, but really need to find out, is... "How much current flows through Wire 3 -- and which way?" You would just measure the current, if your ammeter wasn't broken. Then you remembered the magnetometer that the Tooth Fairy left under your pillow last year, and realized that you could deduce the current in Wire 3 from the measured magnetic field strength! out down wire 1 wire 2 wire