Date:

Author: Linlin Cheng

Subject: Re: displacement current

Post:

Thanks!

On Fri, Oct 31, 2008 at 11:26 AM, Richard Berg wrote:
> Linlin,
>
> It seems to me that this demonstration shows that the capacitance is greater
> with the dielectric oil, therefore the charging current is greater. But it
> does not demonstrate displacement current. To do that you must sense
> something that is occurring between the plates of the capacitor (namely, a
> variation in the electric field or something that varies because the
> electric field is varying).
>
> Our demo attempts to sense the magnetic field created by the changing
> electric field in between the capacitor plates.
>
> I will agree with Wolf, though, that it is arguable.
>
> I still like it as a model to illustrate the situation in three dimensions,
> even if we are not sensing the displacement current.
>
> Dick
>
> On Thu, 30 Oct 2008, Linlin Cheng wrote:
>
>> How about this experiment?
>>
>> Linlin
>>
>> On Thu, Oct 30, 2008 at 11:27 AM, Wolfgang Rueckner
>> wrote:
>>>
>>> Bogus in the sense that (at the time) it was not convincing beyond
>>> reasonable doubt that we were detecting the displacement current.
>>>
>>>
>>>
>>> On Oct 30, 2008, at 1:19 PM, Richard Berg wrote:
>>>
>>>> Wolf,
>>>>
>>>> Bogus in what sense?
>>>>
>>>> Dick
>>>>
>>>> On Thu, 30 Oct 2008, Wolfgang Rueckner wrote:
>>>>
>>>>> I once tried it, and the results were bogus -- Wolfgang
>>>>>
>>>>>
>>>>>
>>>>> On Oct 30, 2008, at 11:38 AM, chuck britton wrote:
>>>>>
>>>>>> so you are saying that Dick's straightforward with clear results is
>>>>>> bogus??
>>>>>> Why would a toroidal iron core be needed?
>>>>>> If Dick's demo had faraday shielding around the plates - would it
>>>>>> still
>>>>>> show results? - would it be more satisfactory to the ney-sayers?
>>>>>> More discussion on this would be appreciated (i.e. I'm too lazy to do
>>>>>> the research)
>>>>>> On Oct 30, 2008, at Oct 30(Thu) 11:17 , Zani, Gerald wrote:
>>>>>>>
>>>>>>> Read Dick Berg's page:
>>>>>>> http://www.physics.umd.edu/deptinfo/facilities/lecdem/services/
>>>>>>> demos/demosk2/k2-63.htm
>>>>>>> I've never had luck with this demo for two reasons. It is tricky to
>>>>>>> do
>>>>>>> correctly. And when I do get it working the Faculty are not
>>>>>>> theoretically
>>>>>>> convinced that the signal is any different from an RF antenna
>>>>>>> signal.
>>>>>>> 1.) To do it the pick-up coil must be a many turns iron core
>>>>>>> Toriod.
>>>>>>> 2.) The AC signal on the cap plates should be of high frequency.
>>>>>>> One handy, free way to get a very high frequency signal is to get an
>>>>>>> old
>>>>>>> VCR player, play a video tape and take the RF signal output out the
>>>>>>> back.
>>>>>>> RF modulators with a 4 MHz bandwidth are commonly found built into
>>>>>>> old VCRs
>>>>>
>>>>>
>>>>
>>>> ***********************************************************************
>>>> Dr. Richard E. Berg, Professor of the Practice
>>>> Director, Physics Lecture-Demonstration Facility
>>>> U.S. mail address:
>>>> Department of Physics
>>>> University of Maryland
>>>> College Park, MD 20742-4111
>>>> Phone: (301) 405-5994
>>>> FAX: (301) 314-9525
>>>> e-mail reberg@umd.edu
>>>> www.physics.umd.edu/lecdem
>>>> ***********************************************************************
>>>
>>>
>>>
>>
>
> ***********************************************************************
> Dr. Richard E. Berg, Professor of the Practice
> Director, Physics Lecture-Demonstration Facility
> U.S. mail address:
> Department of Physics
> University of Maryland
> College Park, MD 20742-4111
> Phone: (301) 405-5994
> FAX: (301) 314-9525
> e-mail reberg@umd.edu
> www.physics.umd.edu/lecdem
> ***********************************************************************
>

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