Transmission through thin layers. In the figure, light is incident perpendicular

Question

Transmission through 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.) Part of the light ends up in material 3 as ray r3 (the light does not reflect inside material 2) and r4 (the light reflects twice inside material 2). The waves of r3 and r4 interfere, and here we consider the type of interference to be either maximum (max) or minimum (min). The table below provides the indexes of refraction n1, n2, and n3, the type of interference, and the wavelength ? in nanometers of the light as measured in air. Give the second least thickness L.

Explanation / Answer

two low to high

2 L = m lambda/n

L = m lambda/(2n)

second least so m = 2

L = lambda/n = 620/1.42= 436.6 nm

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