"A plane capacitor with rectangular plates is fixed in a vertical position...The capacitor is charged and disconnected from the battery...The lower part of the capacitor is now brought into contact with a dielectric liquid [e.g. deionized water]...When
the plates contact the liquid's surface, a force in the upward direction is exerted on the dielectric liquid. The total charge on each plate remains constant."
http://electron6.phys.utk.edu/PhysicsProblems/E&M/2-Dielectrics/capacitors_with_dielectrics.
html
https://www.researchgate.net/profile/Yogendra-Srivastava-2/publication/23709608/figure/fig1/AS:416392504463364@1476287117403/When-parallel-capacitor-plates-are-submerged-into-a-dielectric-fluid-the-Maxwell-upward.png
When a SOLID dielectric is placed between the plates of a capacitor, the attraction between the plates INCREASES, due to polarization of the dielectric.
When a LIQUID dielectric (e.g. deionized water) is placed between the plates of the capacitor, there is polarization again but, paradoxically, the attraction between the plates DECREASES. Why? A pressure in the liquid between the plates emerges that
pushes on the plates and so counteracts the original electrostatic force of attraction (if the capacitor is half-immersed, as in the above case, the pressure lifts water against the gravitational force):
"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."
http://farside.ph.utexas.edu/teaching/jk1/lectures/node46.html
In an electric field, water develops a specific bulk pressure:
Tai Chow, Introduction to Electromagnetic Theory: A Modern Perspective, p. 267: "The strictly electric forces between charges on the conductors are not influenced by the presence of the dielectric medium. The medium is polarized, however, and the
interaction of the electric field with the polarized medium results in an INCREASED FLUID PRESSURE ON THE CONDUCTORS that reduces the net forces acting on them."
http://www.amazon.com/Introduction-To-Electromagnetic-Theory-Perspective/dp/0763738271
Wolfgang K. H. Panofsky, Melba Phillips, Classical Electricity and Magnetism, pp.115-116: "Thus the decrease in force that is experienced between two charges when they are immersed in a dielectric liquid can be understood only by considering the effect
of the PRESSURE OF THE LIQUID ON THE CHARGES themselves."
http://www.amazon.com/Classical-Electricity-Magnetism-Second-Physics/dp/0486439240?tag=viglink21401-20
The additional pressure emerging in an electric field is caused by thermal motion, like gas pressure. This means that, if suitably harnessed, it will do work AT THE EXPENSE OF AMBIENT HEAT. Here is the molecular mechanism behind the pressure:
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRA0IrDVAR8ako9gvxLLmuYYWupOY9zmEmCVvqldbgY9lJj-lhX
If it were not for the indicated (with an arrow) dipole, other dipoles in the picture are perfectly polarized as if there were no thermal motion. Of course, this is an oversimplification – thermal motion is a factor which constantly disturbs the
polarization order. The crucial point is that, as can be inferred from the picture, any thermal disturbance contributes to the creation of a local microscopic pressure. Consider the indicated dipole. It has just received a thermal stroke and has
undergone rotation as a result. Now it pushes adjacent dipoles electrostatically. One can say, somewhat figuratively, that the indicated dipole has absorbed heat and now, by pushing adjacent dipoles, is trying to convert the absorbed heat into work. The
sum of all such microscopic disturbances is macroscopically expressed as bulk pressure.
Water in an electric field, by developing a specific pressure able to power vigorous flows and jets, automatically becomes a perpetual-motion machine of the second kind. It can do mechanical work (e.g. by rotating waterwheels) at the expense of ambient
heat (there is no other source of usable energy), in violation of the second law of thermodynamics.
Pentcho Valev
https://twitter.com/pentcho_valev
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