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Applied Optics

Applied Optics


  • Editor: Joseph N. Mait
  • Vol. 48, Iss. 6 — Feb. 20, 2009
  • pp: 1212–1217

Flashes of light below the dripping faucet: an optical signal from capillary oscillations of water drops

Thomas Timusk  »View Author Affiliations

Applied Optics, Vol. 48, Issue 6, pp. 1212-1217 (2009)

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Falling water drops from a dripping faucet, illuminated from above, exhibit a row of bright strips of light, a few centimeters apart at a fixed distance below the faucet. Flash photographs of the drops show that they are oblate in shape when the flashes occur, and the bright flashes of light originate from the edge of the drop that is on the opposite of the overhead light source. Here we show that the spots result from the same internal reflection that gives rise to the rainbow in a cloud of spherical drops. The periodic flashes reflect the capillary oscillations of the liquid drop between alternating prolate and oblate shapes, and the dramatic enhancement in the oblate phase results from a combination of several optical effects. Ray tracing analysis shows that the flashes occur when the rainbow angle is 42 ° in spherical drops but sweeps over a wide range between 35 ° and 65 ° for typical ellipsoidal drops, and the intensity of the caustic is strongly enhanced in the oblate phase. This phenomenon can be seen in all brightly lit water sprays with millimeter size drops and is responsible for their white color.

© 2009 Optical Society of America

OCIS Codes
(010.0010) Atmospheric and oceanic optics : Atmospheric and oceanic optics
(290.1350) Scattering : Backscattering

ToC Category:
Atmospheric and Oceanic Optics

Original Manuscript: November 10, 2008
Revised Manuscript: January 28, 2008
Manuscript Accepted: February 3, 2009
Published: February 19, 2009

Thomas Timusk, "Flashes of light below the dripping faucet: an optical signal from capillary oscillations of water drops," Appl. Opt. 48, 1212-1217 (2009)

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