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**1. Homework Statement**

A coating of

*n*1 = 1.27 material is to be added to

*n*2 = 1.50 glass, in order to make it "irridescent."

a) What is the thinnest layer of material which will have a reflection maximum for normal-incidence light at BOTH 400 and 600 nm (vacuum) wavelength?

b) This thickness will have a reflection minimum at some wavelength between 400 and 600 nm. What is the wavelength of the reflection minimum?

2. Homework Equations

2. Homework Equations

2*d=lambda(coating), 2*d=lambda(coating)/2

**3. The Attempt at a Solution**

I got the first part correct and the answer was 472 nm but I can't get b right. For b I did 2*d=lambda(coating)/2 since it says that the reflection will be minimum.