|LECTURE DEMONSTRATION MANUAL | Instructional Research Lab : ucla physics|
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E.5.10 Reality of the Vector Potential
In the ideal case the magnetic field lines of a toroidal coil are entirely contained witnin tne coil and = 0 outside. This can be checked by using a flip-coil, Hall probe, or compass needle near the toroidal coil.
However, the lines of vector potential circle the flux lines:
So A is not zero outside the coil.
If a wire is threaded through the hole of the toroid and returned through the hole, case 1, no galvanometer deflection is seen as B is switched on and off. But if the wire is threaded through the hole and returned around the coil, case 2, a galvanometer deflection will be seen from = -d/dt.