Our group was interested in studying lightning in the classroom. Lightning has been shown to be fractal in nature (ref. Brower, Green and Soosaar). Realizing the difficulty of bringing lightning into the room, we decided to look at electrical discharge from a Tesla coil. The fractal nature of the discharge is similar to patterns produced by lightning.
Our first task was to design the apparatus with which to create patterns we could somehow record. We based our technique on the work of one of last year's participants design. Our apparatus was modified to maximize the desired visible pattern. The next step was to record the pattern produced on a camcorder, capture the image and analyze the fractal nature of the pattern.
Build a classroom model to investigate the fractal nature of the electrical discharge from a Tesla coil.
1. Cover the Plexiglas with a thin film of glue in a disk shape at least as large as the diameter of the ring. There is no need to go to the edge of the plate. Use a variety of glue types.
2. Sparsely sprinkle the glue with iron filings.
3. Place a conducting ring in the center of the coated plate.
4. Connect a grounding wire to the ring.
5. Touch the Tesla coil to the metal filings at the center of the apparatus.
6. Set the apparatus in a vertical position. Record the results with a camcorder.
7. Capture and digitize selected frames from the video which exhibit fractal patterns.
8. Analyze the patterns using the Fractal Dimension program.
We initially observed poor results when we tried to display the discharge due to the fact that the iron filings were too densely placed. The glue stick resulted in the best patterns because it produced a thinner film. This film was made less dense by carefully rubbing off some of the excess metal.
We used two different types of conducting rings. The first ring had a diameter of 4.5 inches. The ring was cut out of the bottom of an aluminum pie plate. The center of the ring was cut out leaving a .5 inch band on the outside. It was secured to the apparatus with four large binder clips. The second ring was made from a piece of 18 gauge copper wire formed into a circle and secured under another Plexiglas square with a small hole drilled into the center. The second plastic square is necessary to provide good metal to metal contact. Another piece of copper wire is inserted into the hole. The purpose of the hole is to provide a discharge point for the Tesla coil. Better viewing opportunities existed as a result of holding the Tesla coil on the back side of the apparatus.
We captured and digitized several discharge patterns from the video produced by Glenn Govertsen. We then compared the fractal dimension with that of acceptable values of lightning.
We built a successful model of a spark discharge recording device. We used the computer to determine that the fractal dimension of the spark was 1.39. Most references state that the fractal dimension of lightning is 1.3.
After several successful runs, we are pleased to have worked with a method that gives us the ability to produce, capture and save, then analyze a small scale model of lightning.
Well we walked into the lab kinda cool and slow Charlotte and Nancy were ready to go "I wanna do lightning" said Nancy with a grin Larry and Char wouldn't get another word in . . . Cherry Wheats
We decided "Okay, guess it's worth a try Might be cool to see electricity fly" A lightning bolt, we know its actual, When you analyze it comes out as a fractal . . . Cheery Wheats
With a little help from Peter and Paul And Nancy carrying most of the ball And Charlotte saying "I'll never quit" We captured a nice little photo of it . . . Buck Wheats
We played around and cleaned it nice The discharge image was worth its price We rushed to the lab, came thru the door Measured a fractal dimension of 1.4 . . . Shredded Wheats
Now it's time to make our plates, glued the iron to the glass, gave it a shake Table top got a little messy But we're finally ready to zap it with the Tesly . . . Cream of Wheats
Nancy with the coil and Larry with the plate, And Charlotte kickin' out the ones who tried to spectate Grounded the anode and touched the iron Saw an electric show, it was really fryin' . . . Wheaties
Excited about the demo, could be a lot of fun But not as fun as Boston in the summer sun The work we've done here has not made us weary Au contraire, we've become quite cheery . . . Cherry Wheats