Postby **Osennecho** » February 28th, 2012, 4:24 pm

A question I stumbled upon...

Light of wavelength 500 nm shines on a soap film (n=1.46). For what soap film thickness, other than the minimum thickness, will constructive interference occur?

I have no idea how to start...any help? Thanks!

Constructive interference occurs at odd multiples 1t, 3t,5t, etc where t=thickness and is the following equation: t=λ/(4n). The minimum would be at 1t and thus the next smallest would be at 3t. So multiply the value from t=λ/(4n) by 3 and you should get 257nm.

So destructive interference would occur starting at λ/2n?

I believe so, with deconstructive interference occurring at even multiples (It's actually even 180 degree phase changes and such, which gets to complicated for me to be able to explain without failing miserably so I have simply said even multiples for deconstructive and odd for constructive as that should generally be enough to solve).

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