Date: Fri, 18 Feb 2011 23:33:13

Author: Urs Lauterburg

Subject: Re: Tin Foil Capacitor

Post:

Dear Tap-lers,

I actually show this with a conductive umbrella that I hold in my
hands while standing on an isolated platform. I first charge the
umbrella and myself up to 500VDC in respect to ground by touching a
sphere at 500VDC with the tip of the closed umbrella. Because the
umbrella is connected to a thin leaf electrometer the meter will show
a certain charge. Now, when I open the umbrella the electrometer
reading goes down and when I close it again it comes back up again. I
can cycle through by opening and shutting many times. We ''sell''
this by arguing that the capacitor's surface would increase in
respect to the ground. The effect is there but rather subtile.

I think it corresponds to the rolled up surface describe in the article.

Happy demoing physics

Urs

Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern
Switzerland

>Yes, wire leakage may be a significant problem. Get teflon insulated
>wires or other "low leakage" insulated wires. Keep them well away
>from other surfaces. Make sure the connections on your electometer
>are squeeky clean by washing with alcohol. Any surface that the
>apparatus touches should be an insulator and squeeky clean as well.
>
>Dan Beeker
>
>> From: keith.warren@ncsu.edu
>> To: tap-l@lists.ncsu.edu
>> Subject: Re: [tap-l] Tin Foil Capacitor
>> Date: Thu, 17 Feb 2011 16:59:50 -0500
>>
>> You are keeping your wires off of the table right? I have not tried this
>> demo yet but I know from recent trouble shooting that normal lab wires will
>> discharge an electroscope pretty quick if they are lying on the lecture
>> table. The coating is not rated for such high voltages.
>>
>> -Keith
>> ncsu
>>
>> -----Original Message-----
>> From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
>> Behalf Of Paul Nord
>> Sent: Thursday, February 17, 2011 4:41 PM
>> To: tap-l@lists.ncsu.edu
>> Cc: Paul Nord
>> Subject: Re: [tap-l] Tin Foil Capacitor
>>
>> Dale,
>>
>> You should have tried it last week. Much too warm today. You probably need
>> to be quick or do this with very low humidity.
>>
>> There were a couple of things said in that article that confused me.
>> Perhaps the experts can shed some light on this. In the last paragraph the
>> author mentioned that this effect wouldn't work if you had insulating layers
>> between the rolls of foil. Though he seems to imply 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?
>>
>> Second point of confusion. The entire demonstration is intended to infer
>> that a charged rod has a lower capacitance than a flat sheet. Yet the
>> author suggests that this would not work if the foil were wrapped on a
>> conducting rod. Or was he only intending to say that this wouldn't work if
>> the rod were grounded?
>>
>> Paul
>>
>> On Feb 17, 2011, at 3:24 PM, Dale E. Stille wrote:
>>
>> > Tappers,
>> >
>> > Anybody do the "Tin Foil Capacitor" demo by Frank Noschese that was
>> mentioned on page 621 of the Dec. 2010 TPT. Basically you have a roll of
>> tin foil connected to a electroscope. When you charge the electroscope and
>> then unroll the tin foil the voltage goes down, and when you roll it back up
>> the voltage returns to the original value.
>> > My problem when I try to set this up is the voltage leaks off this at
>> about 1000 V. per minute which make it unusable for me. I have narrowed it
>> down to the fact that the voltage is leaking directly off the tin foil. I
>> imagine there is some trick to making this work like the video that went
>> along with the article but I ain't catching it.
>> > Can somebody clue me in??
>> >
>> > Thanks,
>> > Dale
>> >
>>
>>
>>
>


From tap-l-owner@lists.ncsu.edu Fri Feb 18 19:15:16 2011

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