Calculating the Longest Visible Wavelength for Thin Film Interference

[hayowazzup]

Homework Statement

An oil film (index of refraction no = 1.48) floating on water (index of refraction nw = 1.33) is illuminated from above by white light at normal incidence. The film is 360.0 nm thick.



What is the longest visible wavelength that will be strongly reflected?

What is the longest visible wavelength that will be strongly transmitted?

Homework Equations

2nt = (m + 1/2)λ--constructive
2tn = m λ, with m = 0,1,2,...

The Attempt at a Solution

since visible range=400 - 700 nanometers
the longest visible wavelength for constructive interference ...should it be λ=2t/(2+1/2)
λ=456.24?
and so for the second question i use the second equation?

 

[dlgoff]

Do you know the equation for reflectance? I think if the thickness of the film is 1/4λ then the reflectance is minimum.

 

[hayowazzup]

R= ((n2-n1)/(n2+n1))^2
is it this one?