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CBSE - XII Science - Physics - Wave Optics

Why does oil when kept on a surface shows different colours when viewed thru differernt positions whereas the same oil when kept in a closed metallic can has the same colour irrespective of the position of the observer?

Asked by Venkatesh 30th September 2013, 10:51 PM
Answered by Expert


The reason a rainbow effect is created on oil is because of interference. Oil on a puddle will tend to create a thin film, which can be anything from 10 to 100 molecules thick, so its very thin. Each of them can act like a tiny mirror, so when light hits the surface of an oily puddle, some will reflect off the water under the oil, and some will reflect off the oil layers. 

As light is a wave, if you cause the waves to stop lining up with each other, you can get the up part of one wave aligning with the down part of another wave, and these can cancel out. This is called interference, and it causes a pattern of colours according to how much interference is occurring. Oil films of different thicknesses cause different amounts of interference, so you get a rainbow effect
Answered by Expert 2nd October 2013, 10:52 PM

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