chapter24_slides

chapter24_slides - 3/24/2009 1 Wave Optics The particle...

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Unformatted text preview: 3/24/2009 1 Wave Optics The particle nature of light: basis for ray (geometric) optics But the particle nature of light cannot explain: Interference Diffraction Polarization Need to consider the wave nature of light 3/24/2009 2 Two waves could add (interfere) Constructively (resultant amplitude is greater than those of individual waves) Destructively (resultant amplitude is less than those of individual waves) Conditions for interferences Must be coherent (maintain a constant phase difference) Must have same wavelength Visible light wavelength: 400 ~ 700 nm Old method: A monochromatic light source passes through a narrow slit, then through two slits coherent sources Modern method - Laser The laser produces an intense, coherent, monochromatic beam The laser light can be used to illuminate multiple slits directly 3/24/2009 3 Thomas Young: first demonstrated interference in light waves from two sources in 1801 Bright and dark bands (called fringes) are formed on a screen Constructive interference occurs where a bright fringe appears Destructive interference results in a dark fringe t +1-1 t +2-2 + t t +1-1 t +1-1 t +1-1 + = = 3/24/2009 4 Constructive interference occurs at the center point-The two waves arrive in phase Away from the center, if the two waves arrive in phase: - constructive interference If they arrive out of phase 180 :- destructive interference The relative phase of waves depend on the path they travel. The path difference between the two waves when they reach the screen Constructive interference:- , called the order number- m = , the zeroth order maximum- m = 1 , the first order maximum, etc ) sin( 1 2 d r r m d ) sin( , 2 , 1 , m 3/24/2009 5 Destructive interference:- 180 o out of phase Position of interference pattern on the screen: We have assumed that L >> d >> , and the angle is small ) 2 1 ( ) sin( m d ) sin( ) tan( L L y 1 for ) sin( ) tan( For bright fringes For dark fringes: d m L L y bright ) sin( d m L L y dark ) 2 / 1 ( ) sin( ) sin( ) 2 1 ( ) sin( ) sin( L y m d m d Constructive Destructive 3/24/2009 6 Youngs Double Slit Experiment provides a method for measuring wavelength of the light- measure y, L, and d for m=1 or 2, we can calculate . Strongly supports the wave model of light - It is inconceivable that particles of light could cancel each other (in the case of destructive interference) d m L y bright L=1.2 m, d=0.03 mm The second order (m=2) bright fringe is 4.5 cm from the center What is the wavelength of the light?...
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This note was uploaded on 03/30/2009 for the course PHY 102 taught by Professor Luo during the Spring '08 term at SUNY Buffalo.

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chapter24_slides - 3/24/2009 1 Wave Optics The particle...

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