It is very common to see rainbow patterns when you look at the control surface of a compact disc , and also when you appear atsoap bubblesor a thin film of oil blow on still water supply . All three of these effect are create by constructive and destructiveinterferenceof the light hitting the film .
Think about a very thin plastic film of crude float on water as an model . Whenwhite lightstrikes the film , most of it passes through it , but some isreflectedoff of the top and bottom layers of the film . In the same way , when you digest in front of a window in your house , you could see a reflected image in the window . Most of the light is passing through the window and out of the family , but some is reflected back at you . The light that reflects off the top level of a film of oil travels a slightly shorter length than the light reflecting off the bottom layer , as shown in this image :
In this form , the incoming ray of light enters from the upper left . Part of the light passes straight through the film ( A ) . Part of it reflects off the top layer of the film ( B ) . Part of it reflects off the bottom level of the movie ( C ) .
If the moving picture thickness is on the decree of thewavelength of visible light , theninterferencecan occur . Violet light has a wavelength of about 4,000 angstroms ( hundred - millionths of a cm ) , while red igniter has a wavelength of about 7,600 angstroms , so we are talk about an extremely slender film . As we saw in thequestion on rainbows , clean light is made up of all different colour of light .
If the motion-picture show is just the right thickness , a red light wave ( a sine wave ) will bounce off the top and bottom layer in perfect conjunction , and the two leave sine waves will combine to double the amount of reddish light project :
Or , they may reflect exactly out of phase angle , and red will be eliminated .
On a candle , the surface is mirrored so the rainbow colors are much more intense . ( SeeHow cd Workfor a description of a CD ’s expression . ) In a CD , theanglethat the CD is hold at controls the colors you see – the angle controls the path difference .
