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songoku
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Homework Statement
As shown in the figure below, beams of light whose wavelength in air is 600 nm are perpendicularly incident upon two transparent thin films (A and B) in the same phase. The thickness of A and B is l. The refractive indices of A and B are, respectively, nA and nB. The difference of these two indices (nA - nB) is 6.0 x 10-3, and the refractive index of air is 1.00.
What value should be assigned to film thickness l in order that the two beams of light directly passing through A and B, respectively, without reflection at the film – air boundaries are of opposite phase (i.e. phase difference corresponding to half a wavelength)?
Homework Equations
phase difference = (2 x n x thickness) / λ - 1/2
The Attempt at a Solution
What is the meaning of "in order that the two beams of light directly passing through A and B, respectively, without reflection at the film – air boundaries are of opposite phase (i.e. phase difference corresponding to half a wavelength)"?
The light will be reflected when it travels from air to the film and from the film to air so there will be 4 reflected rays, from left and right side of A and B.
Let say:
reflected ray from lef side of A = light 1
reflected ray from right side of A = light 2
reflected ray from left side of B = light 3
reflected ray from right side of B = light 4
So the question means that light 1 and 2 are in phase and light 3 and 4 are in phase, or light 1 is in phase with light 3 and light 2 is in phase with light 4? Or is it just the same for the two cases?