Thickness of Film:Constructive Interference @ 547nm, n=1.31

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The discussion focuses on calculating the smallest nonzero thickness of a soap film for constructive interference of reflected light at a wavelength of 547 nm and refractive index n=1.31. The formula used is 2t = (m + 1/2)(wavelength/nfilm), leading to a calculated thickness of 104 nm for m=0. Participants confirm that this calculation is correct. The thread also includes a request for verification of the solution. The conclusion affirms the accuracy of the result.
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Homework Statement


Light of wavelength 547nm is incident perpendicularly on a soap film (n=1.31) suspended in air. What is the smallest nonzero film thickness for which reflected light undergoes constructive interference?

Homework Equations


2t = (m + 1/2)(wavelength/nfilm)

The Attempt at a Solution


t = (0+1/2)(547nm/(2*1.31))
t = 104 nm

Is this correct?---------
Could someone please check this as well: https://www.physicsforums.com/showthread.php?t=310439
 
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Anyone?
 
It is correct.
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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