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Q & A: visual ripples from melting ice in soda

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Most recent answer: 11/23/2015
Q:
My wife had a clear soda (around here we call soda "pop") with ice cubes this afternoon, and it appeared that the ice cubes inside were emitting waves, much like when you see heat waves come off a car. But in the liquid. We were unsure what this process was exactly. There are a number of differing factors, but we didn't know what was most relevant. Do the waves (distortion of light) come from a) The cold water (ice) melting into the warmer water, thereby giving differing density levels b) The cold water (ice) melting into the warmer carbonated water, thereby ... I don't know c) The cold water (ice) melting into a sugar/water solution, thereby introducing a dilution and (thus) differing densities? Or is it something else? To reproduce (and eliminate other variables) we could do the following: a) Ice in water b) Ice in seltzer c) Ice in sugar-water or corn syrup-water In any case, we didn't know what process was actually involved such that light would bend variably (in waves, swirling, falling) as the ice melted.
- Jonathan (age 29)
Kalamazoo, MI, USA
A:

Your proposed ideas and experiments sound great. 

Yes, you're seeing ripples of different density, and thus different index of refraction for light. My guess is that the temperature differences aren't responsible for most of what you see, because the density of water is only weakly sensitive to temperature in this range. Sugar water, however, has substantially different density and index of refraction, so what you're seeing are swirls of more and less sugary water before they fully mix. I predict that you won't notice much in pure water.

The light itself isn't really doing anything complicated. It just bends a little a it goes from one refractive index region to another, just like it bends when it goes from air to water or water to glass. The ripples you see come are patterns in the liquid itself, not all that different from the swirls you see as smoke rises from a candle.

Mike W.


(published on 11/23/2015)

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