1051_Physics ProblemsTechnical Physics

1051_Physics ProblemsTechnical Physics - 392 P37.31...

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392 Interference of Light Waves P37.31 (a) The light reflected from the top of the oil film undergoes phase reversal. Since 145 133 .. > , the light reflected from the bottom undergoes no reversal. For constructive interference of reflected light, we then have 2 1 2 nt m =+ F H G I K J λ or m nt mm = + = + 2 12 2 1 45 280 bg af a f . n m . FIG. P37.31 Substituting for m gives: m = 0 , 0 1620 = nm (infrared) m = 1 , 1 541 = nm (green) m = 2 , 2 325 = nm (ultraviolet). Both infrared and ultraviolet light are invisible to the human eye, so the dominant color in reflected light is green . (b) The dominant wavelengths in the transmitted light are those that produce destructive interference in the reflected light. The condition for destructive interference upon reflection is 2 nt m = or m nt == 28 1 2 n m . Substituting for m gives: m = 1 , 1 812 = nm (near infrared)
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