Many questions about results How Far Can Sparks Jump

[smr]

We conducted the experiment How Far Can Sparks Jump.
With nothing between the two metal balls (pinballs 1 1/4"), the distance the sparked jump was consistently about 8 cm.
We put a piece of plastic (like plastic from a baggie) and also a piece of paper (notebook) between the balls. There was no change in how far the spark could jump.
So we thought perhaps we didn't really get to the maximum distance with air, so repeated it multiple times, and using the screwdriver, touched the balls each time in case any charge potential left so we'd get most consistent results. Results still about 8.
When we went to aluminum foil, the space between balls actually could increase, and we thought this was perhaps the aluminum was serving as a good conductor allowing the spark to travel further.
But we don't understand why with plastic & paper there was no change. We would have thought, after studying dielectrics, the space would have decreased.
Can any one help make sense of our results or have any suggestions for us?
The only variable we thought we might try is that today is very warm and humid for January, and later this week it will become seasonably cold again so air in house will be more dry with heater running.
Thanks for any assistance; perhaps we are misunderstanding the principle of dielectric?
Susan.

[kgudger]

Hi Susan:

I'm glad to see you're having pretty good results for this experiment (at least for a couple of the trials You asked:

We put a piece of plastic (like plastic from a baggie) and also a piece of paper (notebook) between the balls. There was no change in how far the spark could jump.

. I looked over the experiment again, and have a couple of questions about these materials. First, is the piece of material large enough that the spark cannot jump around it? Second, are you absolutely certain that the material was not touching either ball? Lastly, you might try thicker insulators to see if that helps. Other than these ideas, I'm not sure why the distance between the balls to get the spark to jump did not decrease. I was really glad to see that you get consistent results for air, and that the aluminum foil increased the distance.

Other than these ideas, I'm not sure why you don't see a change with the insulators. Let us know how it works out.
Keith

[Craig_Bridge]

I have a couple of thoughts in addition to the idea of making sure you use a large enough piece so that the spark can't jump around the test sample. A lot of plastic bags these days have a slightly conductive coating applied so they won't build up large static charges in the processing and packaging equipment. Have you tried a piece of waxed paper? What is the relative humidity and temperature where you are located. Paper materials will absorb moisture.

[smr]

Thanks to each of you for your responses. We'll re run the test again later this week and see what happens.
The day we did the test the humidity outside was very high (soggy/misty day) and in the 60's.
The temps for the week coming are expected to be in 30's with rain early in week; it should be cold and drier by weeks end when we try this again.

[smr]

Hello Again,
Well, we repeated the experiment. This time it was VERY COLD and VERY DRY in the house. The spark travelled pretty consistently about 1/2 inch with air; it increased about 1/8 of inch or so with aluminum, and decreased about 1/8 inch with notebook paper, slightly more with heavy bond paper.
Our question is this: calculating the voltage. If I am understanding this right, this would make our voltage almost 34 kV? Can you give me the specific equation to determine the voltage from the spark distance.
Thanks!!!!

[kgudger]

Hello:

According to the experiment,

the dielectric breakdown voltage of air at standard temperature and pressure is approximately 3000 V/mm

and according to Wikipedia

The dielectric breakdown strength of dry air, at Standard Temperature and Pressure (STP), between spherical electrodes is approximately 33 kV/cm

To answer your question, first calculate in cm or mm your spark gap (1" = 2.54cm), then the voltage is-
V = 33,000 * (gap in cm) or V = 3,300 * (gap in mm).

BTW, you said:

it increased about 1/8 of inch or so with aluminum, and decreased about 1/8 inch with notebook paper

and on the surface this sounds backwards - did you mean that the gap decreased when aluminum was between the spheres and increased when using paper? Thanks and have fun.

Keith

[smr]

I'm now a bit confused. In a previous reply it was stated:

I was really glad to see that you get consistent results for air, and that the aluminum foil increased the distance. -- Keith

Our hypothesis was that aluminum, as a conductor, would actually increase the distance a spark could jump; while paper, wax paper, etc as an insulator, would create a smaller gap in which the spark could jump.

[kgudger]

Hi:

Sorry for the confusion - I was wrong in my last post. When you decrease the dielectric constant (with a conductor) you should be able to jump a larger distance. My apologies.

Keith