PURPOSE: To illustrate Standing waves in a exciting way. rod.

DESCRIPTION: A eight-foot piece of four-inch pipe is closed at one end and has a diaphragm and a speaker across the other end. The pipe is filled with natural gas which escapes from a row of small holes along the top edge of the pipe. When it is lit, a row of small flames forms. The speaker is driven with a wave generator. If the pipe is now driven at one of its natural frequencies, a standing wave is set up in the gas which varies the gas density and thus varies the amount of gas being fed to the flames. The flames no longer burn evenly, but sinusoidal modulated flame envelope. You can drive the speaker different natural frequencies to get different flame patterns. Use a frequency of 300-1000 Hz. The square-wave function works the best.

SUGGESTIONS: Use standard safety precautions when doing this demo. Only do this demo is a large classroom which is next to a outside door. The flame tube must be put outside right after the demo is over. Turn off the gas and let the speaker drive the remander of the gas in the tube out. When the flames go out carefully remove the tube from the classroom and place it outside to cool and off gas.

EQUIPMENT: Standing wave tube, bottle gas with regulator and long tubing, wave generator, and safety equipment.

SETUP TIME: 30 minutes

KEYWORDS: STANDING WAVES IN A FLAME