PURPOSE: To demonstrate standing waves in a circular membrane.

DESCRIPTION: A circular wire loop holds a soap film which is positioned in front of a loudspeaker (the rectangular box to the left 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. Some standing wave patterns are shown below.

SUGGESTIONS:

REFERENCES: (PIRA 3B22.70) See AV list for film loops dealing with vibrations of a circular membrane.

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

SETUP TIME: 5 min.