Reflection by thin layers. In the figure, light is incident perpendicularly on a

Question

Reflection by thin layers. In the figure, light is incident perpendicularly on a thin layer of material 2 that lies between (thicker) materials 1 and 3. (The rays are tilted only for clarity.) The waves of rays r1 and r2 interfere, and here we consider the type of interference to be either maximum (max) or minimum (min). For this situation, each problem in the table below refers to the indexes of refraction n1, n2, and n3, the type of interference, the thinlayer thickness L in nanometers, and the wavelength ? in nanometers of the light as measured in air. Where ? is missing, give the wavelength that is in the visible range. Where L is missing, give the second least thickness or the third least thickness as indicated.

Data for #49:

n1=1.69; n2=1.61; n3=1.54; Type=min; L=2nd; Lamda=395

Explanation / Answer

no low to highs

so min given by

2 L = m lambda/n

2nd means m = 2

2 L = 2 lambda/n

L = lambda/n = 395/1.61= 245.3 nm

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