Date: Thu, 21 Aug 2003 15:34:43 -0400

Author: Wolfgang Rueckner

Subject: Re: dielectric constant of water

Post:

Here's an interesting and surprising (I think) update on my
experimentation. Yesterday I inserted a polyethelyne zip-lock-type
bag between two capacitor plates and measured the change in
capacitance when the bag was filled with water:

capacitance with air between plates = 0.035 nF
capacitance with empty bag between plates = 0.035 nF
capacitance with bag full of water = 4.560 nF, which implies a
dielectric constant of 130 for water

Today I inserted an actual (trade-mark written on it) gallon-size
zip-lock bag between the two plates and found the capacitance to go
up to 7.650 nF, a factor of 219!!

The plastic of the two bags looks and feels the same. The thickness
of the zip-lock is different by a factor of two (zip-lock is 0.05 mm
thick plastic whereas other bag is 0.10 mm thick), but neither of
them alone affect the overall capacitance to any significant amount.
Also, I played around with bag size and placement to get a handle on
the magnitude of edge effects. As expected, they're negligible.

Obviously I will try different kinds of plastic bags now, but my
question is -- what's going on here? One thought was that the
plastic happens to be a polar molecule and the polar water molecules
will be aligned at the inside surface of the bag, giving a
polarization effect with bag alone (never mind putting the whole
shebang in a capacitor). But this polarization would be in the
opposite direction w.r.t. the water on the opposite wall of the bag
and this polarization effect at the water/plastic surfaces would
cancel out. Yes?

Your thoughts?? -- Wolfgang
From cbettis@unlserve.unl.edu Thu Aug 21 16:11:55 2003
Message-ID: <009601c3681f$895882e0$96245d81@lecturedemo>
From: "Cliff Bettis"
To:
References: <8ED3EC78-D407-11D7-8B4F-000393B080FA@valpo.edu>
Subject: Vacuum Bazooka
Date: Thu, 21 Aug 2003 14:32:27 -0500
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I would like to tell you all that my new vacuum bazooka was a big hit. I
have been trying it out and the faculty have been swarming around it. As I
left for a meeting this afternoon, three of them were merrily propelling
ping pong balls throuhg pop cans; in fact they ran me out of victims (cans)
for next week.

Cliff
From KBouff@aol.com Thu Aug 21 21:35:31 2003
From: KBouff@aol.com
Message-ID: <78.45e8383e.2c76cdd9@aol.com>
Date: Thu, 21 Aug 2003 21:37:29 EDT
Subject: Re: Cool optical art
To: tap-l@listproc.appstate.edu
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Dear Matt,
There is a book called the "Magic Mirror" book that is commercially
availabable. I think it is Dover Press, but will check and send that info. It
includes about 20-25 anamorphic pictures. I also have a diagram of how to convert
"regular pictures to anamorphic pictures inh my "Phyiscs of Toys" book. If you
want a copy, let me know.
Karen Bouffard
From wonnell@pha.jhu.edu Fri Aug 22 07:09:16 2003
Date: Fri, 22 Aug 2003 07:11:15 -0400 (EDT)
From: Steve Wonnell
To: tap-l@listproc.appstate.edu
cc: Steve Wonnell
Subject: Re: dielectric constant of water
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Dear Wolfgang,

I wonder whether the capacitance due to the water should be calculated
using the spacing between the inner walls of the plastic bags for the
distance between the plates. You might measure the capacitance as a
function of plate spacing (with the ziploc bag filled with water spanning
the gap) to test for this and to separate the effect of the water from
other effects.

Steve W.



On Thu, 21 Aug 2003, Wolfgang Rueckner wrote:

> Date: Thu, 21 Aug 2003 15:34:43 -0400
> From: Wolfgang Rueckner
> Reply-To: tap-l@listproc.appstate.edu
> To: tap-l@listproc.appstate.edu
> Subject: Re: dielectric constant of water
>
> Here's an interesting and surprising (I think) update on my
> experimentation. Yesterday I inserted a polyethelyne zip-lock-type
> bag between two capacitor plates and measured the change in
> capacitance when the bag was filled with water:
>
> capacitance with air between plates = 0.035 nF
> capacitance with empty bag between plates = 0.035 nF
> capacitance with bag full of water = 4.560 nF, which implies a
> dielectric constant of 130 for water
>
> Today I inserted an actual (trade-mark written on it) gallon-size
> zip-lock bag between the two plates and found the capacitance to go
> up to 7.650 nF, a factor of 219!!
>
> The plastic of the two bags looks and feels the same. The thickness
> of the zip-lock is different by a factor of two (zip-lock is 0.05 mm
> thick plastic whereas other bag is 0.10 mm thick), but neither of
> them alone affect the overall capacitance to any significant amount.
> Also, I played around with bag size and placement to get a handle on
> the magnitude of edge effects. As expected, they're negligible.
>
> Obviously I will try different kinds of plastic bags now, but my
> question is -- what's going on here? One thought was that the
> plastic happens to be a polar molecule and the polar water molecules
> will be aligned at the inside surface of the bag, giving a
> polarization effect with bag alone (never mind putting the whole
> shebang in a capacitor). But this polarization would be in the
> opposite direction w.r.t. the water on the opposite wall of the bag
> and this polarization effect at the water/plastic surfaces would
> cancel out. Yes?
>
> Your thoughts?? -- Wolfgang
>
>
From tomford@thesciencesource.com Fri Aug 22 08:39:30 2003

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