I\'m not exactly sure on where I am going wrong since the formula should be 2nt/

Question

I'm not exactly sure on where I am going wrong since the formula should be 2nt/m. It said it was correct for part b, but not sure what I am doing incorrectly for parts a and c.

A film of MgF2 (n 1.38) having thickness 1.66 x 10 cm is used to coat a camera lens (a) What are the three longest wavelengths that are intensified in the reflected light? (Enter your answers from smallest to largest.) 458 Your response differs from the correct answer by more than 100%. nm 229 nm 153 Your response differs from the correct answer by more than 10%. Double check your calculations. nm (b) Are any of these wavelengths in the visible spectrum? Yes O No Need Help? Read t

Explanation / Answer

(a) Given n = 1.38

Thickness of film t =1.66*10-5 cm = 1.66*10-7 m

General equation for interference in thin film is

            2nt = m

where, m =0,1,2,3,...........

for m = 1 ,

            = 2nt

              = (2)(1.38)(1.66*10-7)

              = 4.5816*10-7 m = 458.16 nm

for m=2,

            = nt

              = 1.38*1.66*10-7 m = 2.2908*10^-7 = 229.08 nm

for m=3,

            = .66nt

              = .66*1.38*1.66*10-7 m = 1.5272*10^-7 = 152.72 nm

From above results, we conclude that the wavelength is decreasing.

so, if m is increases then the wavelength is decreasing.

b)

The results shows that none of the wavelengths in the visible spectrum.

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