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 and r_2 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 n_1, n_2, and n_3, the type of interference, and the thinlayer thickness L in nanometers. Give the wavelength that is in the visible range.

Explanation / Answer

Here, 2L=(m+1/2)/n2               ----------------->   condition for maximum interference

=> 2 * 291 = (m+1/2)/1.68

=>    For m =   1

=>      =   651.84 nm           --------------->   wavelength in visible region .

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