Chapter 36

Chapter 36 - time if their light has a phase relationship...

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Chapter 36 Interference In this chapter we explore the wave nature of light and examine several key optical interference phenomena.

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Diffraction For plane waves entering a single slit, the waves emerging from the slit start spreading out, diffracting.
Young’s Experiment For waves entering two slits, the emerging waves interfere and form an interference (diffraction) pattern.

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The phase difference between two waves can change if the waves travel paths of different lengths. Locating Fringes What appears at each point on the screen is determined by the path length difference L of the rays reaching that point. Path Length Difference: sin L d θ ∆ =
( 29 ( 29 If sin integer bright fringe L d θ λ ∆ = = Maxima-bright fringes: sin for 0,1,2, d m m = = K ( 29 ( 29 If sin odd number / 2 dark fringe L d ∆ = = Minima-dark fringes: ( 29 1 2 sin for 0,1,2, d m m = + = K 1 1.5 1 dark fringe at: sin m d - = = Locating Fringes 1 2 2 bright fringe at: sin m d - = =

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Coherence Two sources can produce an interference that is stable over
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Unformatted text preview: time, if their light has a phase relationship that does not change with time: E ( t )= E cos( ϖ t + φ ). Coherent sources : Phase must be well defined and constant. When waves from coherent sources meet, stable interference can occur. Sunlight is coherent over a short length and time range. Since laser light is produced by cooperative behavior of atoms, it is coherent of long length and time ranges. Incoherent sources : jitters randomly in time, no stable interference occurs, Intensity in Double-Slit Interference ( 29 1 2 sin and sin E E t E E t ϖ φ = = + E 1 E 2 2 1 2 4 cos I I = 2 sin d π θ λ = ( 29 ( 29 1 1 1 2 2 2 Minima when: sin for 0,1,2, (minima) m d m m = +2 = + = K 1 2 2 Maxima when: for 0,1,2, 2 sin sin for 0,1,2, (maxima) d m m m d m m = =2 = = = = K K avg 2 I I =...
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Chapter 36 - time if their light has a phase relationship...

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