Date: Mon, 21 Feb 2011 10:21:48

Author: Thomas Greenslade

Subject: Re: Tin Foil Capacitor

Post:

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In the original 1745 experiment by Pieter van Musschenbroek in
Leiden, he tried condensing the electric fluid into a jar of water. The
water inside the glass jar acted as one electrical coating, and his
sweat, on the outside of the jar, formed the other. The jar therefore
had the capacity to hold electric fluid (or charge, if you want to be
modern...) And it held a lot of charge -- Pieter got a nasty shock when
he put the fingers of his other hand into the water.

In the nineteenth century you bought Leiden jars in pint and quart
capacities from scientific suppliers.

I hope that this answers Syracuse Sam's question!

Tom Greenslade

On 2/21/2011 9:18 AM, Sam Sampere wrote:
>
> Why do we call this a capacitor? We don't call wires capacitors,
> thought they do indeed have stray capacitance? All we're doing is
> taking charge off the electroscope and placing it onto another surface.
>
> I tell my students that an electroscope can be used as a charge meter
> or a voltmeter. If using as a voltmeter, you're simply hooking a
> capacitor up in parallel.
>
> So, what am I missing?? Why all the excitement about this one?
>
> Don't you hook your electroscope to one plate of a parallel plate
> capacitor and move it to see a voltage, I mean, charge, I mean
> voltage, maybe I really mean both, change???
>
> Thanks,
>
> Sam
>
> *From:*tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu]
> *On Behalf Of *Michael Thomason
> *Sent:* Friday, February 18, 2011 3:22 PM
> *To:* tap-l@lists.ncsu.edu
> *Subject:* Re: [tap-l] Tin Foil Capacitor
>
> Here
>
> http://physicslearning.colorado.edu/Website_new/Common/ViewDemonstration.asp?Topic=5&SubSubtopic=5C10.31&DemoCode=5C10.31
>
>
>
> is my tin foil capacitor, manufactured by E B Benjamin, 1800-1914,
>
> Michael Thomason, Director of Physics Learning Laboratories
>
> University of Colorado Boulder Department of Physics
>
> 303-492-7117
>
> thomason@colorado.edu
>
> http://physicslearning.colorado.edu
>
> *From:*tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu]
> *On Behalf Of *Paul Nord
> *Sent:* Thursday, February 17, 2011 8:19 PM
> *To:* tap-l@lists.ncsu.edu
> *Cc:* Paul Nord
> *Subject:* Re: [tap-l] Tin Foil Capacitor
>
> Bill,
>
> It's the last paragraph of the article that has this error.
>
> Here's the citation from December:
>
> Tin foil capacitor
>
> And if it's not bad form to quote the article here:
>
> During the demo, students complete the right col- umn with their
> actual observations and explanations. In addition, the sheet has
> several concluding questions such as, "Why is it important that the
> tube in this demo is made of plastic?"
>
> It might be possible to make another tube that has the foil sandwiched
> between sheets of plastic or paper and then roll up the foil. The
> plastic should insulate the foil layers when it is rolled up, and
> therefore there should be no difference in elec- troscope separation
> when the foil sandwich is unrolled and rolled.
>
> Tom - no reference to your article in the December issue. Here's a
> link to your 1976 article:
>
> 19th century textbook illustrations---VII. Surface charge density
>
>
> Great illustration!
>
> Paul
>
> On Feb 17, 2011, at 6:46 PM, William Beaty wrote:
>
> On Thu, 17 Feb 2011, Paul Nord wrote:
>
> that he has not tried this. Would a coil of a single foil with a
> insulating layer have a higher capacitance than a conducting tube?
> Wouldn't the charge simply move to the outside surface?
>
>
> Yep, all foil parts are at the same potential, so there won't be
> e-fields between the layers. Maybe he meant to use *two* foils to
> create a capacitor, and ground one of them?
>
> (((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))
> William J. Beaty http://staff.washington.edu/wbeaty/
> beaty, chem washington edu Research Engineer
> billb, amasci com UW Chem Dept, Bagley Hall RM74
> 206-543-6195 Box 351700, Seattle, WA 98195-1700
>


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In the original 1745 experiment by Pieter van Musschenbroek in
Leiden, he tried condensing the electric fluid into a jar of water.
The water inside the glass jar acted as one electrical coating, and
his sweat, on the outside of the jar, formed the other. The jar
therefore had the capacity to hold electric fluid (or charge, if you
want to be modern...) And it held a lot of charge -- Pieter got a
nasty shock when he put the fingers of his other hand into the
water.

In the nineteenth century you bought Leiden jars in pint and
quart capacities from scientific suppliers.

I hope that this answers Syracuse Sam's question!

Tom Greenslade

On 2/21/2011 9:18 AM, Sam Sampere wrote:



Why do we call this a capacitor? We don’t call wires
capacitors, thought they do indeed have stray capacitance?
All we’re doing is taking charge off the electroscope and
placing it onto another surface.

I tell my students that an electroscope can be used as
a charge meter or a voltmeter. If using as a voltmeter,
you’re simply hooking a capacitor up in parallel.

So, what am I missing?? Why all the excitement about
this one?

Don’t you hook your electroscope to one plate of a
parallel plate capacitor and move it to see a voltage, I
mean, charge, I mean voltage, maybe I really mean both,
change???

Thanks,

Sam



From:
tap-l-owner@lists.ncsu.edu
[mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of Michael
Thomason
Sent: Friday, February 18, 2011 3:22 PM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] Tin Foil Capacitor



Here

http://physicslearning.colorado.edu/Website_new/Common/ViewDemonstration.asp?Topic=5&SubSubtopic=5C10.31&DemoCode=5C10.31


is my tin foil capacitor, manufactured by E B Benjamin,
1800-1914,


Michael Thomason, Director of Physics Learning
Laboratories
University of Colorado Boulder Department of Physics

303-492-7117
thomason@colorado.edu
http://physicslearning.colorado.edu




From:
tap-l-owner@lists.ncsu.edu
[mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of Paul
Nord
Sent: Thursday, February 17, 2011 8:19 PM
To: tap-l@lists.ncsu.edu
Cc: Paul Nord
Subject: Re: [tap-l] Tin Foil Capacitor



Bill,




It's the last paragraph of the article that has this error.



Here's the citation from December:


Tin
foil capacitor





And if it's not bad form to quote the article here:




During
the demo, students complete the right col- umn with
their actual observations and explanations. In
addition, the sheet has several concluding questions
such as, “Why is it important that the tube in this
demo is made of plastic?”



It might
be possible to make another tube that has the
foil sandwiched between sheets of plastic or paper and
then roll up the foil. The plastic should insulate the
foil layers when it is rolled up, and therefore there
should be no difference in elec- troscope separation
when the foil sandwich is unrolled and rolled.






Tom - no reference to your article in the December issue.
Here's a link to your 1976 article:


19th
century textbook illustrations—VII. Surface charge density



Great illustration!





Paul








On Feb 17, 2011, at 6:46 PM, William Beaty wrote:



On Thu, 17 Feb 2011, Paul Nord wrote:


that he has not tried this. Would a coil of a single
foil with a insulating layer have a higher capacitance
than a conducting tube? Wouldn't the charge simply move
to the outside surface?

Yep, all foil parts are at the same potential, so there
won't be e-fields between the layers. Maybe he meant to
use *two* foils to create a capacitor, and ground one of
them?

(((((((((((((((((( ( ( ( ( (O) ) ) ) )
)))))))))))))))))))
William J. Beaty http://staff.washington.edu/wbeaty/
beaty, chem washington edu Research Engineer
billb, amasci com UW Chem Dept, Bagley
Hall RM74
206-543-6195 Box 351700, Seattle, WA
98195-1700










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From tap-l-owner@lists.ncsu.edu Mon Feb 21 11:48:25 2011

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