Asked by Kid

Is one of the formulas used in "thin film" interference problems 2t = (m + 0.5)(lambda/n_film) OR 2t = (m - 0.5)(lambda/n_film), where t is the thickness of the film? I might have copied my notes down incorrectly in class, because according to internet sources, it is the latter but I have the former with the "+" in the brackets. So I just wanted to confirm the proper formula that I should be using. Thank you.
Answered by Damon
The point is that it differs by half a wavelength :)
Answered by Kid
So in the end, it doesn't really matter at all which one I use? Is there ANY difference that I'll get when solving for unknown values depending on which one I use?
Answered by Damon
That is right. You will get a different number of half waves inside there and it depends what you call m = 1 and m = 0. I would use the convention your teacher used.
If you use the + sign then m = 0 has half a wavelength in the film but if you start at m = 1 you want the - sign to get half a wave in there
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