Question

After a minor oil spill, a think film of oil (1.40) of thickness 450 nm floats on the water surface in a bay.

• (a) What predominant color is seen by a bird flying overhead?
• (b) What predominant color is seen by a seal swimming underwater?

I need help with this problem, can you please show all steps. I know it has something to deal with constructive interference and destructive interference. But I can't tell which to use based off of what the problem gives us. Thanks in advance.

Answer 1

When white light is incident on a thin film, the light which comes from any point from it Will not include the colour whose wavelength satisfies the equation 2tcos r = n, in the reflected system. Therefore, the film will appear coloured and the colour will depend upon the thickness and the angle of inclination. If r and t are constant, the colour will be Uniform. In the case of oil on water, different colours are seen because r and t vary

In the first case,

In order to find the colour of the film we yse the equation,

In the second colour is formed due to the refraction of light from thr lower and upper surfaces of the thin film