silly question but on-topic!

[Bill Martin]

Hello,

What happens to the charge in a polar liquid when it is no longer in the
electric field that charged it? As in "flowing past charged plates".

Bill Martin

 

[Bill Martin]

Wouldn't the energy simply be dissipated in rearranging the polar molecules
back to a less "oraganised" state?

I would "guess" that to be the case, just curious if anyone ever looked
into the situation more than casually.

Bill

 

[Tauno Voipio]

I would "guess" that to be the case, just curious if anyone ever looked
into the situation more than casually.

Bill

That is a simple corollary from the second law of thermodynamics:
The kids' room gets messy by itself, and it takes plenty of energy
to clean the mess.

 

[Bill Martin]

Charging and then discharging a capacitor uses no net energy.

That's what made me curious. It seems like removing the charge from the
system which delivered it may be a different situation...so it has to
"go" somewhere in order to be conserved... consider the following simple
picture:


+V
|
|
------------------- metal plate ----non-conducting tube wall---

--->flowing polar fluid --->

------------------- metal plate ----non-conducting tube wall---
|
|
|
-V

Do you suppose it's possible to measure a current flow across the metal
plates that relates to the bulk flow of the polar liquid through the
"capacitor", if you will?

Bill

 

[Tim Williams]

http://en.wikipedia.org/wiki/Electrohydrodynamics

Whether it's purely dielectric (displacement current only), resistive
(lossy, conductive), ionic or other, this is the general subject which
concerns it.

Note EHD mirrors MHD (magneto-...), and both in turn are closely associated
with plasma physics (where E&M are both very important, because the working
fluid is charged and aligns with electromagnetic fields, and flows at a rate
where magnetic fields are significant).

Tim

 

[Jasen Betts]

Hello,

What happens to the charge in a polar liquid when it is no longer in the
electric field that charged it? As in "flowing past charged plates".

when the field is no longer there brownian motion will stir them up.

 

[Jasen Betts]

That's what made me curious. It seems like removing the charge from the
system which delivered it may be a different situation...so it has to
"go" somewhere in order to be conserved... consider the following simple
picture:


+V
|
|
------------------- metal plate ----non-conducting tube wall---

--->flowing polar fluid --->

------------------- metal plate ----non-conducting tube wall---
|
|
|
-V

Do you suppose it's possible to measure a current flow across the metal
plates that relates to the bulk flow of the polar liquid through the
"capacitor", if you will?

For a current to flow the liquid must accept electrons and "holes" from
the plates I can't see a non-electrolyte doing that.

For an electrolyte the magnetohydrodynamic effect is probably simpler.

 

[Boris Mohar]

I would "guess" that to be the case, just curious if anyone ever looked
into the situation more than casually.

Bill

Making a DC transformer?

 

[Don Lancaster]

Not even wrong.

Charging or discharging a capacitor is typically less than 50%
efficient, unless elaborate heroic measures are taken.

Take a charged 1 microfarad capacitor.
Connect it to a uncharged 1 microfarad capacitor.

Voltage drops to half. Energy drops to one quarter.


--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Tim Williams]

Heroic? One inductor will cyclically charge and discharge a capacitor
with miniscule loss per cycle. Newbies like you should google
"parallel resonant circuit."

The two of you should be more specific. Don, emphasize asymptotic (infinite
time), also a lossy circuit (though not even superconducting resonators are
truely lossless (Q > 1e7) and will decay down to the noise floor over the
span of perhaps minutes).

John, stop jumping on people with one arguably applicable statement when
another was obviously implied (asymptotic vs. quarter cycle time in this
case).

Speaking of which, some day I'm going to make a quasi-resonant gate drive
and revolutionize the world on efficiency (if not necessarily physical
size).

Tim

 

[Tom Del Rosso]

Charging and then discharging a capacitor uses no net energy.

Isn't that derivable from, "climbing up and down a ladder does no work"?

Or does "uses no energy" simply mean that no energy was converted to another
form?

 

[Tim Williams]

If you connect a battery to an uncharged cap, through an inductor and
a diode, the cap gets charged to 2 * Vb, with a beautiful
raised-cosine curve and 100% efficiency. That's the starting point.

What part of "connect a cap to a cap" contains a diode? That's not the
starting point.

Tim

 

[Fred Abse]

Heroic? One inductor will cyclically charge and discharge a capacitor with
miniscule loss per cycle. Newbies like you should google "parallel
resonant circuit."



Not even right.

Why do I get that déja-vu feeling?

 

[Spehro Pefhany]

You don't use diodes? Really, they can be handy.

You can use a switch too, provided you open it at just the right time.


Best regards,
Spehro Pefhany