Date: Fri, 22 Mar 2002 10:48:08 -0600

Author: "Karl I. Trappe"

Subject: Re: Safety of Van de Graaff Generators


Warren: This is a good Tap-L topic. My gut response is that if the
VDG is, itself, safe, then most anything you do with is OK. By
"safe", I mean if you have a dome *small enough* that the capacitance
limits the total charge that can be supplied. I confess that I do
not know a specific number. Perhaps it can be judged by arc length
of the discharge in air, given that its about 8KV/cm of discharge.

Some VDGs have a DC power supply loading the bottom comb (I have one
hidden away). For this kind, it is best to have two multimegohm
resistors in series with the power supply. By having two *in
series*, you provide redundancy in case one fails by shorting out.
That will keep the 10KV from arching directly to *you*!

Of course, if you connect the VDG up to an evacuated tube with metal
electrodes resembling an X-ray tube, then that's a different kind of
unsafe. They can produce X-rays under such conditions.

I would guess that some of our medical physics instructors may have
some interesting input. Karl

> We received the following request from Susan Martin
>( about the safety of Van de Graaff
>generators. Can someone from tap-l please respond to her directly?
>Do you know how I could check on the safety of certain class
>experiments using the VanderGraaf Generator?
>Thank you,
>Warren W. Hein
>Associate Executive Officer
>American Association of Physics Teachers
>One Physics Ellipse
>College Park, MD 20740-3845
>Voice: 301-209-3300
>Fax: 301-209-0845
>E-mail: whein

Dr. Karl I. Trappe Desk (512) 471-4152
Lecture Demonstration Office Office (512) 471-5411
Physics Department, Mail Stop C-1600 Home (512) 264-1616
The University of Texas at Austin
Austin, Texas 78712-1081