Interference

# Interference - Physics 113 Lecture 12 Interference Todays...

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Physics 102: Lecture 20, Slide 1 Today’s Lecture will cover textbook chapters 21, 22 Physics 113: Lecture 12 Interference Physics 113 Dr. Renat Letfullin

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Interference for Light … Can’t produce coherent light from separate sources. (f 10 14 Hz) Single source Two different paths Interference possible here Need two waves from single source taking two different paths Two slits Reflection (thin films) Diffraction *
Physics 102: Lecture 20, Slide 3 Young’s Double Slit Key Idea L Two rays travel almost exactly the same distance. (screen must be very far away: L >> d) Bottom ray travels a little further. Key for interference is this small extra distance. Physics 113 Dr. Renat Letfullin

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Physics 102: Lecture 20, Slide 4 d Path length difference = d θ Young’s Double Slit Quantitative θ θ d sin θ Constructive interference Destructive interference (Where m = 0, 1, 2, …) sin(θ) tan(θ) = y/L Physics 113 Dr. Renat Letfullin
d Path length difference = d θ Young’s Double Slit Quantitative θ θ Destructive interference    dsin θ = (m + 1 2 ) λ Constructive interference    dsin θ = m λ where m = 0, or 1, or 2, ... d sin θ Need λ < d

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Physics 102: Lecture 20, Slide 6 d Destructive interference    dsin θ = (m + 1 2 ) λ Constructive interference    dsin θ = m λ where m = 0, or 1, or 2, ... Young’s Double Slit Quantitative y sin( θ ) tan( θ ) = y/L d L m y λ = d L m y λ + = 2 1 θ L θ A little geometry… Physics 113 Dr. Renat Letfullin
Physics 102: Lecture 20, Slide 7 Summary of Young’s Double Slit Concept Screen a distance L from slits Single source of monochromatic light λ d 2 slits- separated by d L At points where the difference in path length is 0, λ ,2 λ , …, the screen is bright .

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