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A coaxial cable consists of an outer conductor and an inner conductor separated by an insulating plastic filler. These two conductors usually carry equal currents in opposite directions. You may have seen this type of configuration on cable TV hookups as well as on certain types of computer networks. The animation shows the progression of the magnetic fields as many small wires are added to produce a coaxial configuration (position is given in millimeters and magnetic field strength is given in microtesla, 10^-6 T). Restart.

1. Build the coaxial cable by adding the current-carrying wires. Explain why this type of cable might be preferable to household wiring or lamp cord which consists of two side-by-side wires carrying currents in opposite directions.
2. Explain why the field is zero outside the cable and within the center (blue) cable.
3. Click-drag to measure the field at any point. Find the current passing through the inner conductor.

Problem authored by Melissa Dancy, Mario Belloni and Wolfgang Christian.