A force field, an energy field ... a field of dreams. (Don't forget to dream.)
Harry Stephen A. Lawrence wrote: > > > Michel Jullian wrote: >> Paul, Paul, Paul you missed my point again, never mind :) >> >> To go back to your pet theory, since as you said the formulae for >> field energy and potential energy are the same, there are in fact at >> least three equivalent ways to describe the same thing: field energy, >> or potential energy, or work done by the forces. > > A minor nit to pick: Potential and field energy may be interchangeable > for electric fields, but apparently not for magnetic fields. Permanent > magnetic dipoles have potential energy = -mu.B which is not tracked by > the total field energy. Case in point: If the field of one dipole has > energy E, then the fields of two widely separated dipoles have total > energy 2E. Let them pull themselves together until they touch end to > end -- the potential energy drops, but the total field energy increases, > to about 4E, as the two fields overlap almost exactly. (The energy > density goes as field intensity squared, so halving the volume while > doubling the intensity yields a net energy increase of 2x). > > So if we include permanent magnets in the picture, it's going to be > awkward to replace PE with field energy everywhere. I think this may be > what led Paul to assert that nobody knows where the energy comes from in > this case.
