Tesla at the Magnet Lab

"Conducting" Electricity

The large Tesla coil shown here was producing about 250 kV at 200 kHz. The presence of an aluminum rod nearby alters the spark pattern because the current being carried off by the sparks is drawn to the grounded conductor rather than something like the overhead lights up by the ceiling.



The sparks look purple because of the emission lines from nitrogen gas. (The spark results when air molecules, mostly nitrogen, get ripped apart by the high voltage. The current is carried by a plasma.) A bare hand works almost as well as an aluminum rod, since your body is a conductor.



At high frequencies (such as 200,000 Hz), the current flows over the surface of the body. The only risk is from a burn at the point of contact. Based on the reaction of one other demonstrator, you can definitely feel it. This photo was really spectacular. The yellow spots you see are where it is burning his hand.

Important Note:
Frequency is the difference between life and death. A low frequency (such as 50 or 60 Hz) Alternating Current would be fatal at those voltages. That would go through your body and, partly because it is so well matched to the frequency our nervous system operates at, would stop the heart. In contrast, we easily get 200 kV from a van de Graaff generator in lecture demos, but the resulting small Direct Current only produces a painful shock.

Musical Reindeer

The sparks emanating from a small stuffed reindeer sitting on a smaller Tesla coil produced music. (Click the photo for a much bigger version.)



What was happening was that the air gets heated by the glowing discharge you see in the photo. If the intensity of the sparks varies at 5000 times per second (too fast to see or photograph), you get a sound wave of 5000 Hz produced in the air instead of the crackling sound of the sparks. They modulating the amplitude of the voltage delivered to the coil (and putting wires in the stuffed animal to produce many sharp points for spark production) with a music source, and you hear music.

The music went away, or was altered, if a rod was used to draw off the current in a single spark rather than the discharge you see here. Very nice.