Date: Tue Sep 25 17:12:14 2007

Author: Richard Heckathorn

Subject: Re: Electrostatics and humidity


Harry Meinor's set of demo books has a number of different plans to build a dirod apparatus. Information starts on page 850. Plans start on page 1312. I almost completed the one shown in Fig A29-91 a number of years ago but...

On page 1189 is a circular flame tube 4 ft in diameter. I think I saw one in operation at a physics meeting held in Troy NY. The 8 ft straight flame tube in shown on page 495.


Helping teachers who facilitate, motivating students who learn.
Dick Heckathorn 14665 Pawnee Trail Middleburg Hts, OH 44130 440-826-0834
Adjunct Physics Teacher - Baldwin Wallace College
Physics is learning how to communicate with ones environment so that it will talk back.

-----Original Message-----
From: [] On Behalf Of William McNairy
Sent: Tuesday, September 25, 2007 3:22 PM
Subject: Re: [tap-l] Electrostatics and humidity

Does anyone know of a commercial source for the Dirod Generators?


John Hubisz wrote:
> When I moved from Nova Scotia (even though it rained most of the time,
> it was easy to do electrostatics experiments) to the Texas Gulf Coast
> where it was hard, I got a Dirod Electrostatic Generator which always
> (well, it had to be treated as described below on occasion, but not
> too often) worked.
> John Hubisz
> Bernard Cleyet wrote:
>> I've posted this before, but possibly on another list. When I taught
>> at a C. C. on a bluff overlooking the Pacific, rarely dry and salt
>> free, I used a small semi-portable refrigeration dehumidifier at one
>> end of the bench. It blew dryer air at the apparatuses. The
>> difference was very noticeable *. They are very much less expensive
>> than what was contemplated below Dodds' answer.
>> * The difference between working well and not working!
>> bc
>> Stan Dodds wrote:
>>> Lowering the humidity will certainly help with electrostatics, but
>>> 40% is pretty dry. You may find that the cost cutters won't let you
>>> do this because your AC bill will get very large. Worse, if they
>>> decide to maintain conditions only when the lab is in use and let it
>>> go over weekends you will get drastic humidity cycling, which leads
>>> to condensation and corrosion on everything. (They tried this here a
>>> few years ago, and nearly destroyed a bunch of machine tools in our
>>> shop.)
>>> An alternative, which works well in delightfully damp Houston is to
>>> use insulators that don't wet well. Following suggestions from Frank
>>> Peterson at Iowa State, we've had good luck with polyethylene and
>>> teflon. Nylon and PVC are almost as good. Various of these materials
>>> are used to insulate electroscopes, make rods for charging, and
>>> insulate the parts of a Faraday ice bucket. The experiments work in
>>> the oldest building on campus, even when it's 80 degrees and
>>> raining outside.
>>> It's also important to keep the surfaces of the insulators clean.
>>> Anything that has been touched becomes hygroscopic and salty,
>>> creating a discharge path. Wiping with isopropyl (rubbing alcohol)
>>> or methyl alcohol removes the crud and restores the insulation. If
>>> you hold a fairly wet wiper in your bare hand and ground yourself,
>>> you will also conduct away any charge that may be trapped on the
>>> surface you are cleaning. Very useful for quantitative charge
>>> transfer measurements.
>>> Good luck.
>>> Stan
>>> On Sep 20, 2007, at 12:18 PM, David Maiullo wrote:
>>>> Hi Tappers,
>>>> Interesting question from this gentleman from Dallas. If you know a
>>>> lot about this subject, and think you can help him, please email
>>>> him directly as I'm not sure that he is on tap-l. You could copy
>>>> us, too, if you'd like!
>>>> BTW, I'm not a Prof, I just play one on TV.......
>>>> ;>)
>>>> Dave
>>>> Paul MacAlevey wrote:
>>>>> Dear Prof. Maiullo,
>>>>> I�d like to ask you a question. My students do electrostatics
>>>>> investigations in all seasons in our labs in Dallas. I am involved
>>>>> in making environmental specifications for some Physics labs in a
>>>>> new building. Should we pay more attention to absolute humidity or
>>>>> relative humidity when doing these experiments? My proposal was
>>>>> for conditions of relative humidity 40�5 % and temperature 70�5 �F
>>>>> (giving an absolute humidity of about 7 g/m^3). Do you think that
>>>>> these conditions will work? Can you point me to any literature on
>>>>> the subject that I might have overlooked?
>>>>> Take care,
>>>>> Paul MacAlevey
>>>>> Physics Dept, Founders Building, FO 2.708B
>>>>> University of Texas at Dallas
>>>>> phone: (972)883-4634
>>>>> e-mail:

Dr. William McNairy, Lecturer Phone: (919) 660-2689
Lecture Demonstration Coordinator FAX: (919) 660-2525
Department of Physics, Duke Univ. e-mail
Box 90305
Durham, NC 27708-0305

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