A thin film of polystyrene of refractive index 1.49 is used as a nonreflecting c

Question

A thin film of polystyrene of refractive index 1.49 is used as a nonreflecting coating for Fabulite (strontium titanate) of refractive index 2.409.

Part A

What is the minimum thickness of the film required? Assume that the wavelength of the light in air is 440nm .

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A thin film of polystyrene of refractive index 1.49 is used as a nonreflecting coating for Fabulite (strontium titanate) of refractive index 2.409.

Part A

What is the minimum thickness of the film required? Assume that the wavelength of the light in air is 440nm .

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Explanation / Answer

The reflected rays must be ?/2 out of step so that they don't reflect.

There will be a phase shift as each reflection so they cancel out and the only path difference will come from the thickness of the film. And the wavelength will shorten in the film so

?/2 =

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