334CHAPTER 24 24.68Phase reversals occur in the reflections at both surfaces of the oil layer, so there is zero net phase difference due to reflections. The condition for constructive interference is then 2brightnfilmtmmnλ==(1) and the condition for destructive interference is 11222darknfilmmn=+(2) Solving for the order number, m, in equation (1), and substituting into equation (2) gives the film thickness as ()500 nm313 nm4 1.201500 nm 750 nm41darkfilmdarkbrighttnλλ=−−24.69(a) Assuming that nin the figure at the right, Ray 1 undergoes a phase reversal as it reflects at point A, but Ray 2 has no reversal as it reflects at B. Therefore, the condition for
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