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Wavelengths->calculating m

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wavelengths-->calculating "m"

A thin film of turpentine (n=1.36) covers a lanthanum flint glass plate (n=1.80). What is the minimum thickness the film should have if it is to appear green (wavelength=560nm) when viewed from above in white light? (answer=206nm)


Use the equation 2t(n)=mλ



I know that it would be 2t(1.36)=1(560), but why is "m" 1? I know that there is a 180 degree phase change making the waves constructive...but does m=1 only because there needs to be some light emitted?
 
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because you have to find minimum thickness, thickness is directly proportional to m and m can only be an integer :wink:
 

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