Text: [Magnetics] We have introduced A because it does have an important physical significance. Not only is it related to the energies of currents, as we saw in the last section, but it is also a "real" physical field in the sense that we described above. In classical mechanics it is clear we can write the force on a particle as F = q(E + v X B), so that, given the forces, everything about the motion is determined. In any region where B = 0 even if A is not zero, such as outside a solenoid, there is no discernible effect of A. Therefore for a long time it was believed that A was not a "real" field. It turns out, however, that there are phenomena involving quantum mechanics which show that the field A is in fact a "real" field in the sense we have defined it.

See Also: FULL HARMONIC CHORD, SCALAR FIELD, LATENT FORCE

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