Date/Time
Date(s) - 12/02/2014
3:30 pm - 4:30 pm

Title: The Rainbow and the Dripping Faucet: Optical Signals from Capillary Oscillations of Water Drops

Speaker: Dr. Tom Timusk

Institute: McMaster University

Location: ABB 102

Description:

Falling water drops from a dripping faucet, illuminated from above, exhibit bright spots of light, a few centimeters apart, at a fixed distance below the faucet. High speed photography shows that the drops are oblate in shape when the ashes occur. The flashes originate from the edge of the drop on the opposite to the light source and the light takes the same path through the drop as the rays that give rise to the rainbow in spherical drops. The periodic ashes reflect the capillary oscillations of the liquid drop between alternating prolate and oblate shapes. Ray tracing analysis shows that the dramatic enhancement in the oblate phase results from a combination of several optical effects and the flashes occur because the rainbow angle (42◦ in spherical drops) sweeps between 35◦ and 65◦ as the drops oscillate. The intensity of the effect 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. If all drops were oblate, an elliptical rainbow would result. Look for it!