01_23_Light_Interference_Beats

01_23_Light_Interference_Beats - Today 1/23 o Today...

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Unformatted text preview: Today 1/23 o Today: Young’s Double Slit experiment, Text 27.2 Beats, Text 17.4 o HW: 1/23 Handout “Young’s Double Slit” due Monday 1/24 o Friday: Phase Shifts on Reflection, Text 27.3 (See fig 27.11) o Peer Guidance Center 1-4 Mon-Thur Wit 211 (Not 209) Young’s Double Slit (like two speakers) Single frequency source Wave crests λ Wave troughs Dark and bright “fringes” on a screen In phase at the slits c c c c c d d d d Always true for any interference problem Sources In Phase: Constructive if PLD = m λ Destructive if PLD = (m + 1 / 2 ) λ Sources Out of Phase: Constructive if PLD = (m + 1 / 2 ) λ Destructive if PLD = m λ PLD = “path length difference” m = 0, 1, 2, 3,… (I used “n” the other day) Two slit geometry (screen far away) Screen PLD = d sin θ (d = slit separation) θ d θ θ PLD d (close enough) Two slit geometry Screen PDL = d sin θ (d = slit separation) θ d sin θ = m λ constructive interference d sin θ = (m+ 1 / 2 ) λ destructive interference When the sources (slits) and “in phase” d A simpler picture Screen very far away (L) Two slits very close together (d) θ d sin θ = m λ constructive interference d sin θ = (m+ 1 / 2 ) λ destructive interference When the sources (slits) and “in phase” The m’s m = 0 m = 1 m = 2 m = 1 m = 2 m = 1 m = 0 m = 0 m = 1 d sin θ = m λ d sin θ = (m+ 1 / 2 ) λ 0 “zeroth order” fringe 1 “first order” fringe 2 “second order” fringe Distance between fringes, y m = 0 m = 1 m = 2 m = 1 m = 2 m = 1 m = 0 m = 0 m = 1 L y θ tan θ = y / L Example:...
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01_23_Light_Interference_Beats - Today 1/23 o Today...

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