Magnetic field from two wires distance

  • Thread starter fisixC
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  • #26
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Yes, zero. For a coaxial cable, the wires are located along the same axis with radial symmetry, allowing us to use Ampere's Law. Since the currents had equal magnitudes and were opposite in direction, the net enclosed current was zero and thus the net B-field is zero.

For the earlier problems, the wires were not located on the same axis. Note the distance to the point we were calculating the magnetic field at was different for each wire's B-field. Also, you can't use Ampere's Law in the fashion we did for the coaxial cable, because there's no longer the symmetry. We can apply it for each individual wire, so the result is the B-fields will not cancel each other out.