🚀 go-pugleaf

On Sep 22, 5:19 am, Pentcho Valev <pva...@yahoo.com> wrote:

> If a constant-charge parallel-plate capacitor is totally immersed in
> water, the force of attraction between the plates is 80 times weaker
> than the force of attraction in vacuum. However, if we thrust some
> solid dielectric between the plates (not necessarily occupying the
> whole distance between them - it could be rather thin), the force of
> attraction becomes even greater than in vacuum. Accordingly, the
> following four-step cycle (carried out very slowly) violates the
> second law of thermodynamics:
>
> 1. Plates are immersed and fixed. We thrust the solid dielectric.
> 2. Plates get closer. We GAIN work.
> 3. We withdraw the solid dielectric.
> 4. Plates get apart; initial state restored. We SPEND work.

  Specifically, more work is done removing the dielectric than was
gained by inserting it.

> When the plates are immersed in a liquid dielectric (water), some
> additional pressure between them emerges, pushes them apart and so
> counteracts their electrostatic attraction (W. Panofsky, M. Phillips,
> Classical Electricity and Magnetism, Addison-Wesley, Reading,
> Massachusetts (1962), pp. 111-116). If the plates are vertical and
> only partially immersed, the same pressure forces the liquid between
> the plates to rise above the surface of the water pool (see fig. 6-7
> on p. 112 in Panofsky's book). What if one punches a small hole in one
> of the plates, just above the surface of the pool? Will the lifted
> water leak through the hole and fall? If lifting is due to an
> additional pressure generated within the bulk, as assumed by Panofsky
> and Phillips, then water WILL leak through the hole and the second law
> will be violated. No matter how weak the waterfall is, theoretically
> it can rotate a waterwheel

  Panofsky's assumption is false. Water is lifted into the gap because
water molecules are polarizable, and are drawn from a region of
curved, weak electric field lines (near, but outside the plates'
edges) into a region of strong, straight electric field lines (between
the plates).

  The plates are not "pushed apart" by the water. The attractive force
is not "counteracted"; it is lessened because much of the field's
energy is used to rotate the water molecules to line up with the
field, and keep them that way. Notice the amount of "lessening" is
numerically the same as water's dielectric constant. This is NOT a
coincidence.

  Your conclusion is false, as you would see if you knew anything
about electrostatics, or if you cared enough to actually build a
simple capacitor and DO THE EXPERIMENT. Evidently though, you care
more to see your words in print than to extend yourself to doing a
little trivial physics.

  Water will not "leak" out of a hole in one of the plates because THE
ELECTRIC FIELD IS NOT CONFINED TO THE SPACE BETWEEN THE PLATES.

  A water molecule between the plates near the hole's edge will be in
a region of curved field lines and will therefore feel a resultant
REPULSIVE force from the hole. To "fall" out of the hole, a water
molecule would have to climb "up" the increasingly curved field lines,
then rotate 180 degrees, but it will then feel a force PUSHING IT BACK
IN THE HOLE due to the field from the other plate "reaching around"
the plate with the hole.

(wishful thinking snipped)

> Take a suspended and stretched spring. It can lift a weight as it
> contracts, that is, we GAIN work. However, in order to restore the
> initial stretched state of the spring, we must SPEND work so there is
> no net gain. If both contraction and stretching are carried out in a
> reversible fashion, the net work gained at the end of the cycle is
> zero.

  No, the "net work gained" is NEGATIVE. You will have to do work to
make up for that lost as heat.

> Consider again a suspended and stretched spring but this time it is
> "chemical", that is, we have one of the macroscopic contractile
> polymers described by Dan Urry in:
>
> http://pubs.acs.org/doi/abs/10.1021/jp972167t
> J. Phys. Chem. B, 1997, 101 (51), pp 11007 - 11028
> Dan W. Urry, "Physical Chemistry of Biological Free Energy
> Transduction As Demonstrated by Elastic Protein-Based Polymers"
>
> If, before contraction, we add acid (H+) to the system, the force of
> contraction and, respectively, the work gained as the polymer
> reversibly contracts increase. Then, just before stretching, we remove
> the added H+ from the system: the force of contraction and,
> respectively, the work spent as we reversibly stretch the polymer
> decrease. At the end of the cycle, THE NET WORK GAINED FROM
> CONTRACTION AND STRETCHING IS POSITIVE.

  No, it is not, THE "NET WORK GAINED" FROM CONTRACTING AND STRETCHING
IS NEGATIVE.

  The words "Free Energy" in the referenced paper DO NOT mean that
energy is gained for free.

> So far things go against the second law of thermodynamics

  Only for those who wilfully misunderstand the meaning of the words
"free energy" in the paper.

>but the
> complete account requires that the net work gained from adding H+ to
> and removing H+ from the system be evaluated. If it is positive or
> zero, the second law is definitively violated. If it is negative, the
> second law is saved for the moment.

  No, it is not "saved for the moment", it is yet again demonstrated
to be correct.

> In the absence of the polymer, adding H+ to and removing the same
> amount of H+ from the system, in a reversible fashion, would amount to
> zero net work gained. The polymers designed by Urry, however, release H
> + as they contract, and absorb H+ as we stretch them.

  For the polymers to absorb H+ ions work must be done on the fibers,
for the polymers to expel the ions the fibers must do work on the
ions.

> It is easy to
> see (for people experienced in electrochemistry at least) that this
> makes the net work gained from reversibly adding H+ to and then
> removing the same amount of H+ from the system POSITIVE.

  No, it is not. The same amount of work is done by the polymers to
expel the ions as was done on stretching them, minus the irreducible
small amount of energy that WILL be lost as heat.

  There is NOT a positive energy balance.

> Conclusion: The reversible cycle:
>
> 1. The polymer is stretched. We add H+ to the system.
> 2. The polymers contracts and lifts a weight.
> 3. We remove the same amount of H+ from the system.
> 4. We stretch the polymer and restore the initial state of the
> system.
>
> violates the second law of thermodynamics.

  No, it does not.


  Mark L. Fergerson