Spark-in-a-Jar
Project Overview
Spark-in-a-Jar was the simple-sounding name given to a complex lab project. The project was the final mark for Junior Lab, the toughest physics lab one can take at Geneseo. To test breakdown voltage characteristics at different pressures and in different gases my partner, Louis Caves, and I needed to construct a complicated apparatus consisting of a vacuum jar and an air compressor. We also needed high voltage.
Quest for High Voltage
Right off the bat, we were denied the use of high voltage power supplies in the lab. Fortunately, from some junked appliances we were able to find 120V, 60Hz transformers. We connected them in parallel, which gave us more turns and stepped up the 120V, 15A outlet to nearly 4.3kV, 0.5A. At the time, I did not realize the danger in doing this but our precautions were sufficient enough to not get electrocuted. We used the metal base of the vacuum chamber as ground so that anything external to the chamber could not be energized. This also allowed us to just set the copper anode wire on the base of the jar, which made it easier to move to get different gap distances.
Project Achievements
In the limited 5-week timeframe we were able to come up with, design, and build the apparatus. Ultimately, we were able to present results of the study to the physics department. In fact, we had a few extra days. In the video, a marshmallow can be seen in the jar. In our extra time we discovered that vacuum jar electric arcs toast marshmallows better than any other method. Due to the reduced pressure, the marshmallow expands and has more surface area to cook, meaning more of the marshmallow is toasted. Secondly, because there is little to no oxygen, it cannot catch on fire! Although rotating it is difficult, considering the high voltage.
Original Vacuum Jar Anode/Cathode Setup in Operation
Close-up of low pressure arc gap