Lecture 21 Notes

# Lecture 21 Notes - Recap of last lecture For small the...

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Recap of last lecture For small θ the maximas are at 2t = m λ n where λ n = λ 0 /n Maxima for 2t=(m+ ½) λ m=0,1,2… Minima for 2t = m λ Phase shift of λ /2

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An air wedge between two glass plates Just like the thin film, two waves reflect back from the air wedge in close proximity, interfering as they go. Phase shift of λ /2 Maxima when net phase shift = 2t+ λ /2 =m λ or 2t = (m- ½) λ m=1,2,3,… or 2t=(m+ ½) λ m=0,1,2…
Amongst these 4 situations which ones will yield a maxima if 2L = (m+ ½) λ /n 2 A. a B. b C. c D. d 1.4 1.6 1.8 b) 1.8 1.6 L 1.4 c) 1.5 1.3 L 1.4 d) 1.4 1.6 L 1.5 a)

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Problem 35.54 There is half-cycle phase change upon reflection on the top surface But not for the bottom, so for constructive interference for λ 1 and λ 2 , where these wavelengths are in glass. The two different wavelengths differ by just one 11 1 12 2 22 2( ) ( ) tm m λλ = += + 21 -value, 1. m mm = 1 1 1 2 1 1 () 2 2 2 2( ) mmm m λ ++  + = = ⇒=   01 1 477.0 nm 540.6 nm 1 17(477.0 nm) 8. 2 8 1334 nm. 2(540.6 nm 477.0 nm) 2 4(1.52) m tt n +  = = = + =   White light reflects at normal incidence from the top and bottom surfaces of a glass plate (n = 1.52). There is air above and below the plate. Constructive interference is observed for light whose wavelength in air is 477.0nm. What is the thickness of the plate if the next longer wavelength for which there is constructive inteference is 540.6nm?
Newton’s rings Bright rings when net phase shift = 2t+ λ /2 =m λ or 2t = (m+ ½) λ and dark rings when 2t = m λ m=0,1,2,…

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Newton’s rings
You perform the Newton’s Ring experiment with white light instead of monochromatic light, you should see A. No rings B. Larger spacing between rings C. Smaller spacing between rings D. Rings of different color E. Need more information

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You perform the Newton’s Ring experiment with white light instead of monochromatic light, you should see A. Rings of different
Using fringes to test quality control • An optical flat will only display even, concentric rings if the optic is perfectly ground.

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Lecture 21 Notes - Recap of last lecture For small the...

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