Physics
posted by Marissa .
So I'm having some trouble with this problem.. Is there an equation or is it just a ratio? I'm having so many problems with this one!
THANKS!
What is the minimum thickness of coating which should be placed on a lens in order to minimize reflection of 531 nm light? The index of refraction of the coating material is 1.32 and the index of the glass is 1.57.

Read "single layer reflection coatings" at
http://en.wikipedia.org/wiki/Antireflective_coating#Singlelayer_interference_coatings
You need 1/4 wavelength thickness at a refractive index of 1.32
At 531 nm and index 1.32, the wavelength of light is 531/1.32 = 412 nm
The coating thickness should be 1/4 of that 
that's what i thought, too. but it's not.
2n(material)t= m*(wavelength/2)
going from a medium with higher n to lower n, you divide the wavelength by 2.
thanks for the help, though. i eventually figured it out!
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