When viewing a piece of art that is behind glass, one often is affected by the light that is reflected off the front of the glass (called glare), which can make it difficult to see the art clearly. One solution is to coat the outer surface of the glass with a thin film to cancel part of the glare.

Requried:

a. If the glass has refractive index of 1.62 and you use TiO2, which has a refractive index of 2.62 as the coating, what is the minimum film thickness that will cancel light of wavelength 505 nm?

b. If this coating is too thin to stand up to wear, what other thickness would also work? Find only the three thinnest ones.

Question

Physics

Ricky Bradford

10 June, 17:54

When viewing a piece of art that is behind glass, one often is affected by the light that is reflected off the front of the glass (called glare), which can make it difficult to see the art clearly. One solution is to coat the outer surface of the glass with a thin film to cancel part of the glare.

Requried:

a. If the glass has refractive index of 1.62 and you use TiO2, which has a refractive index of 2.62 as the coating, what is the minimum film thickness that will cancel light of wavelength 505 nm?

b. If this coating is too thin to stand up to wear, what other thickness would also work? Find only the three thinnest ones.

+1

Answers (1)

Know the Answer?

Mariela Vaughn · Answer 1

This is the case of interference in thin films. The coating has higher refractive index than glass so for destructive interference by reflected light the condition is,

2μt = nλ

where t is thickness of film, μ is refractive index of the film

2 x 2.62 x t = 1 x 505 (n = 1 for thinnest layer)

t = 96.37 nm

for n = 2, n = 3

thickness = 96.37 x 2 nm

or 96.37 x 3 nm

= 192.74 nm or

289.11 nm.