Spinning Soap Film
Safety Warnings
Warning: Soap Containment
Purpose
Demonstrates thin-film interference in a rotating soap film. Centrifugal force creates a parabolic thickness profile, producing concentric colored rings that evolve as the film thins. Students observe the connection between film thickness and interference color.
Figure 1:
Time sequence under white light showing interference patterns evolving as the spinning film develops a parabolic thickness profile. Colors shift as the film thins from center outward.
Figure 2:
Under colored flood light illumination, interference fringes appear with higher contrast. The concentric ring pattern (lower right) clearly shows the radial thickness gradient.
Figure 3:
Setup with gooseneck lamp for white-light illumination. The cup mounts on the rotator's accessory arm, with the glass dish of soap solution below for dipping.
Figure 4:
Alternative setup with a colored flood light for enhanced contrast. The colored illumination makes interference fringes more visible, especially on camera.
Demo Apparatus
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