# Lect19 - Wave Optics(2 of 2 Second lecture on Chapter 25...

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11/9/11 1 Wave Optics (2 of 2) Coherence and condi,ons for interference Michelson Interferometer Thin Flms Single slit Double slit (con,nued) Single slit – analysis Di±rac,on gra,ngs 11/9/11 Physics 104, Fall 2011 Physics 104 Lecture 19 Nov. 9, 2011 Second lecture on Chapter 25 Interference Lecture Demonstrations: 1. Two sound speakers on some frequency: notice interference when speaker pair is rotated or receiver (you) moves. 2. Double slit 1. Red laser makes larger pattern than green laser (lambda 633nm vs 530nm) 2. Determine wavelength from observed interference 3. Single slit interference 4. Diffraction gratings with red laser: vary d and number of slits) 5. White light on diffraction grating (small d): sharp central white maximum, color separation of Frst maximum (angle for red about 1.5 times larger than angle for blue)

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11/9/11 2 Young’s Double-Slit Experiment Double Slit Analysis Analyze path difference. Assume W is very large The difference in length between the paths of the two rays (of the same wave, d is small) is: Δ L = d sin θ Constructive interference: d sin θ = m λ , m = 0, ±1, ±2, … Destructive interference: d sin θ = (m + ½ ) λ , m = 0, ±1, ±2, … Intensity falls off with increasing angle
11/9/11 3 Double-Slit Intensity Pattern The angle В varies as you move along the screen Each bright fringe corresponds to a different value of m Negative values of m indicate that the path to those points on the screen from the lower slit is shorter than the path from the upper slit Constructive interference: d sin θ = m λ , m = 0, ±1, ±2, … Destructive interference: d sin θ = (m + ½ ) λ , m = 0, ±1, ±2, … The Double Slit Concept November 11 Physics 104, Fall 2009 6 Single source of monochromatic light λ d L At points where the difference in path length is 0, λ , 2 λ , …, the screen is bright. At points where the difference in path length is the screen is dark .

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## This note was uploaded on 11/30/2011 for the course PHYSICS 104 taught by Professor Dasu/karle during the Fall '11 term at University of Wisconsin.

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Lect19 - Wave Optics(2 of 2 Second lecture on Chapter 25...

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