Optics / interference in thin films

[johnj7]

Homework Statement

A soap bubble n=1.33 is floating in air. If the thickness of the bubble wall is 115 nm, what is the wavelength of the light that is most strongly reflected

Homework Equations

2nt=(m+0.5)(lambda)

The Attempt at a Solution

most strongly reflected = constructive interference
t=115 nm
lambda = unknown
n = 1.33
assumption m=0
plug and chug to get lambda

so I got the answer, but I was confused on why we make the assumption that m=0, couldn't m technically be any integer number? Do we just automatically assume that m=0 for "most strongly reflected" if a specific desired wavelength is not given?

thank you!

 

[mgb_phys]

Yes, strictly speaking the question should have said, what is the longest wavelength that is most strongly reflected.
However if you use m>0 you will get wavelengths that are outside the visible band.