312CHAPTER 24 24.14With filmairn>n, light reflecting from the front surface of the film (an air to film boundary) experiences a 180° phase shift, but light reflecting from the back surface (a film to air boundary) experiences no shift. The condition for constructive interference in the two reflected waves is then 12filmnt m2λ=+with m0, 1, 2,=…For minimum thickness, , giving 0m=min4filmtn=(a) With 656.3 nm and 1.330filmn==, ()min656.3 nm123.4 nm41.330t(b) When 434.0 nm and 1.330filmn, min434.0 nm81.58 nmt24.15Light reflecting from the upper surface undergoes phase reversal while that reflecting from the lower surface does not. The condition for constructive interference in the reflected light is then
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