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PROBLEM SET 9

# PROBLEM SET 9 - OPTICAL PROPERTIES OF MATERIALS Light is an...

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MSE 110 - UA • Light is an electromagnetic wave. An electric and magnetic field oscillating perpendicular to the direction of propagation. OPTICAL PROPERTIES OF MATERIALS •The charge particles constituting the material interact with the oscillating electric field. This interaction leads to the optical properties of materials. •When light enters a solid, it can be partly reflected at the surface, transmitted through, absorbed or scattered.

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MSE 110 - UA Refractive index OPTICAL PROPERTIES OF MATERIALS • Hence such glasses have high reflectivity R and glitter like diamond. 2 1 1 + = n n R • Large atoms such as Pb and Zn contains many electrons and therefore have large diffuse electronic clouds easily polarizable (high ε ). • Since , glasses containing Zn or Pb have large refractive indexes. ε = n • The ability of the electronic cloud to distort under an electric field is called polarizability . = n • The polarizability is quantified by the dielectric constant ε , hence • The refractive index n also represent how much the interaction slows down the wave when it enters the material: v c n = c: velocity of light in air v: velocity of light in solid
MSE 110 - UA Light interaction with solids • Four things can happen when light proceeds into a solid. OPTICAL PROPERTIES OF MATERIALS I o I R • Part of the light can be reflected by the surface of the solid. Reflection I o I T • Part of the light can be transmitted through the solid. Transmission I o I A • Part of the light can be absorbed by coupling into the solid. Absorption I o I S • Part of the light can be scattered by the atoms and defects in the solid. Scattering • Therefore, for an incident beam of intensity I o entering the solid: I o =I R +I T + I A +I S

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MSE 110 - UA OPTICAL PROPERTIES OF MATERIALS I R I o 2 1 n 1 n R + = •Reflection •Scattering E r μ r o S I a I 4 λ = •Absorption l α = e o I I I o I •Transmission Absorption Wavelength λ optical window 100
MSE 110 - UA Problem 1 Which of the three following glasses do you expect to be the most highly reflective? [answer A, B, C, D] A- 52 SiO 2 -5 ZnO-21 B 2 O 3 -14 Na 2 O- 8 CaO B- 34 SiO 2 -42 PbO-10 B 2 O 3 -5 Na 2 O- 9 CaO C- 32 SiO 2 -24 ZnO-18 B 2 O 3 -12 Na 2 O- 14 CaO D- 46 SiO 2 -24 PbO-12 B 2 O 3 -11 Na 2 O- 8 CaO 2 1 1 + = = n n I I R o Ans: Glass B has the highest content of lead and therefore will have the highest density, the highest refractive index and therefore will be the most reflective according to:

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MSE 110 - UA Problem 2 Which of the following glasses do you expect to have the smallest dielectric constant? [answer A, B, C, D] A-SiO 2 B-13 SiO 2 -87 PbO 2 C-33 SiO 2 -37 ZnO 2 D-42 SiO 2 -28 PbO 2 -20 ZnO 2 ε = n Ans: The refractive index of a material increases with its density. The glass A has the lowest content of lead and zinc and therefore will have the lowest density and the smallest refractive index and therefore will have the smallest dielectric constant according to:
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PROBLEM SET 9 - OPTICAL PROPERTIES OF MATERIALS Light is an...

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