Odds and ends

[Mark]

I got a 2 X 2 sheet of 1/4 inch thick low density polyethylene in the mail today from Enco. It's a little thick I guess because with my Leyden jars the sparks are long but have less pop or zest. So I tried charging two large aluminum plates separated by the thick sheet. In the past I had been using 1 foot squares of 1/8 inch thick sheets of teflon, polycarbonate, and a gray PVC square. My acrylic I had wider sheets. I find some of the things I buy don't work as planned. "ha"
So the plate results were much like my little pint Leyden jar with the 4 inch diameter brass sphere atop. And too, I don't know if it's just a coincidence but both the pint jar and the plate capacitor effect seem hard to capture on camera. I did two takes of it discharging tonight with a very loud but short spark and neither was caught by the camera. So when I went to look at the clips I just took, you hear it but don't see it, there's a faint hint of a flash in one. But I saw the bright fat sparks and heard the extra loud noise - I really wanted to capture it. No sense in posting a sound without the visual though - alas. As mentioned several of the pint jar takes were also void of the spark. I wonder if those designs make a faster spark; is there such a thing? Maybe they don't last as long. Or maybe I was just unlucky with those two guys. Funny how both refuse to make long sparks. I can't gap them out much.
It took about 50 strokes to get the aluminum discs to fire. Another thing, when I had the plates a little too far from the titanium tubing, I couldn't make the setup spark but when I decided to stop filming, the thing was still crackling like a egg in a hot skillet from being charged up. The interaction of the aluminum plates and LDPE dielectric is interesting in that respect, when it was as charged as it was going to get. I figured I had better not touch it just yet. ha
One other thing, there is a fair amount of surface area with the two plates, they're a little over 16.5 inches in diameter. Maybe I should have saved the crackling clip, the crackling capacitor effect. I thought it might decide to fire on it's own it was so alive. ha
r = 8.25 in
C = 51.836278784232 in
A = 213.82464998496 in2

Factors affecting capacitance (plate area, plate spacing, dielectric material)
http://www.allaboutcircuits.com/vol_1/chpt_13/3.html

There's another plate under the LDPE and a long copper bar/rectangle that the titanium pipe is resting on. I didn't use a ball bearing for the plates to arc over to being lazy I guess. So they just had the round titanium tubing surface area to attract the spark. Bearings probably would have teased out a little longer spark. There's also a short ~3 inch long cylinder of aluminum bar stock inside the end of the titanium tubing if you are wondering what that is. I was planning to make a linear pulsejet and just left it in there after lathing it to fit the tubing.

[Mark]

Another variation on a theme. Still I couldn't get a good picture of the spark after 5 more tries. Funny today I stopped charging and filming it and it fired on it's own at least 15 seconds later. I didn't get the strange crackling sound as I did late last night. I swear there must be some other secret factor that determines how well these things charge. The temperature and the humidity were about the same, very close to 52%. Maybe some windy night air has more life or something.
Parallel Plates Charged with Paper and Plastic.AVI
http://www.youtube.com/watch?v=AU8YXEF-EeE

[Mark]

Parallel Plate Capacitor Discharging.AVI
http://www.youtube.com/watch?v=M88GAbSqgV4

[Mark]

There are 2 very good charts at the very bottom of this page on dielectric constants and dielectric breakdown voltages. It's even got human body parts such as ears rated. I wonder how an ear capacitor would go over on youtube? ha
Your choices are not always obvious as to what is best, taking all characteristics into account and coming up with an answer. Some materials are sometimes specifically made for electrical grades, teflon for example I saw on another site being sold in several grades, depending on your needs. And look at polyethylene and polystyrene. Also methanol as a dielectric constant is not bad, way better than teflon it looks like.
But what's really interesting to me is ice, (see chart on dielectric constants) maybe I could freeze my aluminum plates with an ice layer and then charge up the aluminum-ice eskimo sandwich and see how it does. ha
Finally, some materials are easier to excite than others and this affects what to choose from too. There're so many qualities each material has it's not so clear cut as to what's really the best or best in some specific application. Something with a very high dielectric breakdown voltage is going to be thinner or you can get away with using thinner material which affects capacitance, the closer the plates the better. There's more than I understand or can make sense of yet.
http://physics.info/dielectrics/

[Mike Everman]

I hope you make an ice capacitor! That would rank up there with the clay pulsejet.

[Mark]

I wonder how a frozen disc of salt water and then pure water and then another salt water disc would do or if it would work at all? Or maybe you could use powdered aluminum or iron in some suspension/colloid and freeze it for the conducting plates. It would probably work great in Antarctica. ha
In that one book on Homemade Lightning, it details an elaborate process and combination of substances for making the dielectric like they used to do before the invention of plastics.

[Mark]

"Voss, Wimshurst and Carré machines are all electrostatic induction devices. In effect, they are all examples of a continuous electrophorous . In the latter, an initial charge on an insulated dielectric disk induces a charge of the opposite sign on an insulated conductor."
http://physics.kenyon.edu/EarlyApparatu ... chine.html
http://physics.kenyon.edu/EarlyApparatu ... chine.html

When writing to Joseph Priestly in 1775 Allesandro Volta (1745-1827) noted that it was a device that "electrified but once, briefly and moderately, never loses its electricity."
http://physics.kenyon.edu/EarlyApparatu ... orous.html

[Mark]

"The forked acoustic tube, invented by William Hopkins (1793-1866) about 1835, is used to detect the relative phasing of adjacent sections in a Chladni Plate. As one of these sections is moving upward, creating a compression in the air above it, the other is moving downward, producing a rarefaction. The open legs of the tube are placed over the adjacent segments, and sample the signals. Since they are 180 degrees out of phase, the signals cancel, and no sound comes from the tube. If you cover one of the legs with your hand, the sound will be clearly audible. The sound will be louder if the two legs are positioned over two segments of the Chladni plate which are in phase."
http://physics.kenyon.edu/EarlyApparatu ... pkins.html

[Mark]

The apparatus was designed to illustrate the asymmetry of discharges from positive and negative points. The 1923 Leybold catalogue calls this "Gaugains's valve apparatus for showing that positive electricity passes more easily from a point to a plate, negative on the contrary passes more easily from a plate to a point."
http://physics.kenyon.edu/EarlyApparatu ... arges.html

[Mark]

"He invented the sound-wheel in 1876, but very graciously yielded precedence to the Austrian, V. Dvorak, who, it was found later, had quite independently made the same device a few months earlier. This little instrument ... consists of four small tuned resonators attached to a small cross and balanced on a pivot. When placed near a source of continuous sound of the pitch to which the resonators are tuned, such as an electrically driven tuning fork, the reaction against the closed end by the stationary wave formed inside of each resonator causes the wheel to rotate "backwards."
http://physics.kenyon.edu/EarlyApparatu ... rbine.html

[Mark]

"It must have been a great surprise to see a 150 pound student supported by a column of water reaching only 2.4 ft above the level of the platform."
http://physics.kenyon.edu/EarlyApparatu ... radox.html

[Mark]

Just an odd process, I wonder how he arrived at the technique?
"Boys formed the fine quartz fiber by attaching one end of a rod of quartz to an arrow, and the other to a solid object, melting the middle portion of rod of quartz in a hot flame, and shooting off the arrow; this method he described in 1887. "
http://physics.kenyon.edu/EarlyApparatu ... meter.html

"When thermal radiation falls on the blackened copper disk, the thermo-electric junction produces a current in the copper loop. This feels a magnetic torque, and the suspended system twists. A very light mirror is attached to the bottom of the quartz fiber to allow the rotation to be followed. The funnel rotates, and allows radiation to be directed toward the disk."

"Using this instrument with a 16 inch reflecting telescope, Boys was able to observe thermal radiation from a candle at a distance of up to three miles."

[Mark]

Imagine feeling your way in the dark in those early days. Guess they will say that about us in a few hundred years too.

"In letters written in 1776-77 the Italian physicist Alessandro Volta (1745-1827) described a new form of Eudiometer, which is a device for testing the "goodness" of air. In its most useful scientific form, this was a stout glass tube of constant inner diameter closed at the top, where two electrodes passed through the glass and formed a spark gap. The lower end of the tube was placed in a dish of water, and the air to be tested was introduced into the tube and its volume noted. A known volume of hydrogen was then let into the tube, and the mixture ignited by static electricity. The experiment could then determine the goodness of the air (the oxygen content) from measurements of the volume of the remaining gas."
http://physics.kenyon.edu/EarlyApparatu ... meter.html

"Volta's Pistol developed from the Eudiometer, a device developed by Alessandro Volta in 1776-77 to study the "goodness" or oxygen content of air. Volta himself suggested the construction of an inflammable air gun in which a spark fired a mixture of hydrogen and oxygen. By the middle of the 19th century the scientific instrument had turned into a piece of lecture demonstration apparatus. The loud bangs produced by these demonstrations as the cork stopper blew out of the end could awaken even the dullest students."
http://physics.kenyon.edu/EarlyApparatu ... istol.html

[Mark]

Soda Can Leyden Jar
http://www.instructables.com/id/Soda-Ca ... Jar/#step1

[Mark]

Electrophorus - Fondazione Scienza e Tecnica, Florence
http://www.youtube.com/watch?v=0vbStOvf ... re=related