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Pentcho Valev
When two opposite charges, or the plates of a capacitor, are immersed in water, the attraction between them decreases considerably. W. Panofsky and M. Phillips ("Classical Electricity and Magnetism", Addison-Wesley, Massachusetts, 1962, pp. 111-116) explained the effect in terms of a very strange PRESSURE that develops between the plates. This pressure seems to be non-conservative, gas pressure-like ("the decrease in force.... cannot be explained by electrical forces alone"), pushes the plates apart and so counteracts the original electrical force of attraction. If the plates are only partially immersed (fig. 6-7 on p. 112), the same pressure pushes the liquid between the plates upwards so that this liquid rises high above the surface of the pool.

I don't know if Panofsky and Phillips or someone else described the non-conservative pressure for the first time. In any case, in my view, this is the greatest discovery of 20th century physics (although for the moment few people would care). It can be shown that the partially immersed plates (fig. 6-7 on p. 112 in Panofsky's book) form a device that violates the second law of thermodynamics. See more in

Pentcho Valev
QUOTE (Pentcho Valev+Apr 13 2006, 04:12 PM)
("the decrease in force.... cannot be explained by electrical forces alone"),

Finally, a Pento Valev post that has nothing to do with Einstein. And a quote from a nearly-modern textbook, very good. Let's see what we can find to elucidate.

Dielectric liquids in electrostatic fields (Here we use classical fluid mechanics with classical electromagnetism and just a hint of Bohr-level atomic theory, but essential the same point is made for a pre-Rutheford atomic theory. If you are not familiar with fluid dynamics, it's one of those fields where simple axioms lead to complex math.)

QUOTE (Richard Fitzpatrick+)
According to Eqs. (3.54) and (3.104), if a sphere of dielectric liquid is placed in a uniform electric field  then the pressure inside the liquid takes the constant value
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It is clear that the electrostatic forces acting on the dielectric are all concentrated at the edge of the sphere and are directed radially inwards; i.e., the dielectric is compressed by the external electric field.
As is well known, when a pair of charged (parallel plane) capacitor plates are dipped into a dielectric liquid the liquid is drawn up between the plates to some extent. Let us examine this effect. ... Making use of the boundary conditions that  and  are constant across a vacuum/dielectric interface, we  [obtain]
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This electrostatic pressure difference can be equated to the hydrostatic pressure difference rho_m g h to determine the height h that the liquid rises between the plates.
Let us consider another paradox concerning the electrostatic forces exerted in a dielectric medium. Suppose that we have two charges embedded in a uniform dielectric [epsilon]. The electric field generated by each charge is the same as that in vacuum, except that it is reduced by a factor [epsilon]. Therefore, we expect that the force exerted by one charge on another is the same as that in vacuum, except that it is also reduced by a factor [epsilon]. ...  from the point of view of electrical interaction alone there would appear to be no change in the force exerted by one capacitor plate on the other when a dielectric slab is placed between them (assuming that [sigma] remains constant during this process). ... However, in experiments in which a capacitor is submerged in a dielectric liquid the force per unit area exerted by one plate on another is observed to decrease ... This apparent paradox can be explained by taking into account the difference in liquid pressure in the field filled space between the plates and the field free region outside the capacitor. ...  The sum of this pressure force and the purely electrical force (3.110) yields a net attractive force per unit area
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acting between the plates. Thus, any decrease in the forces exerted by charges on one another when they are immersed or embedded in some dielectric medium can only be understood in terms of mechanical forces transmitted between these charges by the medium itself.

As you see there is nothing wrong with Pencho Valev's quote, or the source that he takes it from (Fitzpatrick also cites it as reference material ). "cannot be explained by electrical forces alone" seems to be a direct appeal to the equations of motion of a fluid, which is outside the scope of many electomagnetics textbooks.

The effect (electrostriction in dielectric liquids) appears to be known before the 20th century, as per:
"Note on the Complete Scheme of Electrodynamic Equations of a Moving Material Medium, and on Electrostriction" Joseph Larmor, 1898, Proceedings of the Royal Society of London, 63,, pp. 365-372

You might want to consider
"An experimental analysis of electromagnetic forces in liquids" DG Lahoz and G Walker, November 1975, Journal of Physics D: Applied Physics, 8, 16, pp. 1994-2001

I think electostriction is actually used in many of today's ink-jet print heads, but I have no current sources for that. Oh, wait, here it is:

Finally, if Pencho Valev wants to construct a perpetual motion machine using this principle, he is welcome to. I will not try and claim he stole my idea should he ever become the richest man in Bulgaria.
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