Date: Mon, 21 Feb 2011 09:20:46

Author: David Maiullo

Subject: Re: Tin Foil Capacitor

Post:

Urs,

Is this your "Mary Poppins" demo?

;-)

Very clever and cute.

Dave/RU

On 2/18/2011 5:33 PM, Urs Lauterburg wrote:
> 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 Mon Feb 21 09:40:11 2011

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