How to Determine Minimum Thickness for Dark and Bright Spots in Soap Films?

[Motox]

Homework Statement

Light of wavelength 580 nm strikes a soap film (n=1.33), which is surrounded by air. What is the minimum thickness needed to produce
a) dark spot?
b) bright spot?

Homework Equations

n1/n2=wavelength 2 / wavelength 1

2t = m (wavelength) <-- dark
2t = (m + 1/2) (wavelength) <--- bright

 

[ideasrule]

Those equations are right. Just plug in the numbers are you're done.