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- Homework Statement:
- A fine metal foil separates one end of two pieces of optically flat glass, as in the figure(Figure 1). When light of wavelength 640 nm is incident normally, 35 dark lines are observed (with one at each end).

- Relevant Equations:
- 2t/lamba = m/2

hi,

i know you have to use 2t/lambda= m/2 to get the answer of 10.9 um. However i was taught that there would be phase difference caused by reflection, since n1(air)< n2(glass). SO the equation in my head would be 2t/lambda - 1/2= m/2. Can someone explain why i'm wrong?

i know you have to use 2t/lambda= m/2 to get the answer of 10.9 um. However i was taught that there would be phase difference caused by reflection, since n1(air)< n2(glass). SO the equation in my head would be 2t/lambda - 1/2= m/2. Can someone explain why i'm wrong?

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