Date: Fri, 25 Feb 2011 08:13:20

Author: Zani, Gerald

Subject: Re: Best commercial VDG

Post:

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Urs,

The radius of the dome determines the length and size of the spark.

Larger dome, more capacitance, larger spark.

Because the larger radius dome has lower surface charge density and
therefore has a lower electric field strength. So it accumulates more
charge capacity before the discharge occurs.

Small dome produces a small sparks. A needle point will not produce any
spark but does allow for a high electric field, high surface charge density
and a continuous discharge.

On Fri, Feb 25, 2011 at 5:36 AM, Urs Lauterburg <
urs.lauterburg@space.unibe.ch> wrote:

> Dear Tap-lers,
>
> Thank you again for all the inputs about hyping up my Science First VDG. I
> did take it into the dark but could not see a distinct discharge corona,
> although I did hear a faint bristling noise. I was not really able to locate
> the source of it. It seemed to come from different places. I also tried the
> electrostatic wind test William Beaty suggests in his online write-up. I did
> not want to stick my nose to close to the dome because though because I
> didn't really feel like getting zapped right into my face. I have not
> noticed any unusually strong winds either, except the one produced by the
> moving belt maybe.
>
> In any case by zapping I always meant to a grounded metal sphere. In fact I
> found out that the shape of the ground terminal you want to zap at does
> indeed matter a lot and that this probably was the problem to begin with.
> Because I used another than the usual 12cm diameter metal sphere for the
> ground terminal, I used a smaller one with a brass fixture that has a rather
> sharp rim. So possibly the problem was a smaller buildup of potential due to
> excess leakage with that smaller sphere. When I used the 12cm sphere again
> things seems to be back to what I consider the normals range with arcs of
> about 15 to 20cm ( 6 to 9'') sparks. Do you think that's normal in dry air?
> I wonder if the sparks would be even longer between the VDG dome and one of
> the discharge wands Science First offers specially to pair their VDGs. There
> seems to be two kind of wands a 90cm No 615-3135 large and a 45cm No
> 615-3115 small one. I wonder if the diameter of the wand's spheres are the
> same for both models. Any experimentally determined data like the ark
> lengths between the VDG and the wands on this?
>
> Happy charged & sparking physics
>
> Urs
>
> Urs Lauterburg
> Physics demonstrator
> Physikalisches Institut
> University of Bern
> Switzerland
>



--
Gerald Zani
Demonstration Manager
Physics
Brown University
(401) 863-3964

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Urs,The radius of the dome determines the length and size of the sp=
ark.Larger dome, more capacitance, larger spark.Because the=
larger radius dome has lower surface charge density and therefore has a lo=
wer electric field strength.=A0 So it accumulates more charge capacity befo=
re the discharge occurs.

Small dome produces a small sparks.=A0 A needle point will not produce =
any spark but does allow for a high electric field, high surface charge den=
sity and a continuous discharge.On Fri, =
Feb 25, 2011 at 5:36 AM, Urs Lauterburg wrote:

Dear Tap-lers,

Thank you again for all the inputs about hyping up my Science First VDG. I =
did take it into the dark but could not see a distinct discharge corona, al=
though I did hear a faint bristling noise. I was not really able to locate =
the source of it. It seemed to come from different places. I also tried the=
electrostatic wind test William Beaty suggests in his online write-up. I d=
id not want to stick my nose to close to the dome because though because I =
didn't really feel like getting zapped right into my face. I have not n=
oticed any unusually strong winds either, except the one produced by the mo=
ving belt maybe.



In any case by zapping I always meant to a grounded metal sphere. In fact I=
found out that the shape of the ground terminal you want to zap at does in=
deed matter a lot and that this probably was the problem to begin with. Bec=
ause I used another than the usual 12cm diameter metal sphere for the groun=
d terminal, I used a smaller one with a brass fixture that has a rather sha=
rp rim. So possibly the problem was a smaller buildup of potential due to e=
xcess leakage with that smaller sphere. When I used the 12cm sphere again t=
hings seems to be back to what I consider the normals range with arcs of ab=
out 15 to 20cm ( 6 to 9'') sparks. Do you think that's normal i=
n dry air? I wonder if the sparks would be even longer between the VDG dome=
and one of the discharge wands Science First offers specially to pair thei=
r VDGs. There seems to be two kind of wands a 90cm No 615-3135 large and a =
45cm No 615-3115 small one. I wonder if the diameter of the wand's sphe=
res are the same for both models. Any experimentally determined data like t=
he ark lengths between the VDG and the wands on this?



Happy charged & sparking physics

Urs

Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern
Switzerland
-- Gerald ZaniD=
emonstration ManagerPhysicsBrown University(401) 863-3964

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From tap-l-owner@lists.ncsu.edu Fri Feb 25 08:48:12 2011

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