Standing Waves On A Soap Film


To demonstrate standing waves in a circular membrane.


Point source, soap film ring with soap solution, oscillator and speaker.

Setup Time

5 min




A circular wire loop holds a soap film which is positioned in front of a loudspeaker (the rectangular box to the right of the soap film). It is illuminated by a bright point source which casts a reflected pattern on the screen as shown in the photograph. A sine-wave oscillator attached to the speaker can be tuned to obtain various standing wave patterns, which are defined by the bright lines in the reflected light.


David T. Kagan and Louis J. Buchholtz, Demonstrations of normal modes on a bubble membrane, AJP 59, 376-377 (1991).