Vikas TU
Last Activity: 12 Years ago
Strong reflection is referring to constructive interference between rays reflected off the top and bottom of the film.
There is a phase shift of ½λ for rays reflected off the top of the film (reflection against a more dense medium)
There is no phase shift with reflection off the bottom of the film (reflection against a less dense medium)
Reflected rays off the top will combine constructively when alongside waves having a path difference of ½ wave (or 1½, 2½ ....) caused by travelling through the film.
The minimum thickness (t) for a path diff. of ½ wave is given by ..
2 t = ½ λ'' .. (λ'' = wavelength in film = λair / n)
t = ¼( λ / n) .. .. 0.25 x 589^-9m / 1.25 .. .. ?t = 1.18^-7 m
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