Physics: Principles and Problems

Chapter 19: Interference and Diffraction


Every cloud ... It is said every cloud has a silver lining. The cloud photographed to the right certainly has a bright one. What light phenomenon is at work here to produce such a brilliant border? Reflection and refraction do play a role, but so does diffraction— the bending of light around an edge. In a cloud, the edge that light bends around is the surface of a water drop.
Refraction Just before the light beam exits the water drop, it "clings " to the droplet's outer surface just for an instance; this is diffraction.
		Sometimes colors can be seen around the edges of clouds or in thin, wispy clouds. Clouds displaying colors like this are called iridescent clouds. Diffraction bends the light, but what causes all the colors to form?

		Cloud droplets are smaller and more uniform towards the edge of the cloud, partly due to ongoing evaporation. Inside the cloud, droplets are more likely to bump and coalesce into different sized drops. Explain how uniform drops at a clouds edge would help the formation of iridescent clouds.
		To read more about the physics atmospheric phenomena, go to http://ww2010.atmos.uiuc.edu/(Gh) /home.rxml. Clicking will launch a new window.