Lecture21

# Lecture21 - PHYSICS 220 Lecture 21 Waves Textbook Sections...

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Lecture 21 Purdue University, Physics 220 1 Lecture 21 Waves Textbook Sections 11.6 - 11.10 PHYSICS 220

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Lecture 21 Purdue University, Physics 220 2 Overview • Last Lecture – Wave Types • Transverse (e.g. pulse on string, water) • Longitudinal (sound, slinky) – Harmonic • y(x,t) = A cos( ω t – kx) or A sin( ω t – kx) – Superposition • Add amplitudes • Today – Reflection and Refraction – Interference and Diffraction – Standing Waves
Lecture 21 Purdue University, Physics 220 3 Superposition

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Lecture 21 Purdue University, Physics 220 4 • The net disturbance is the sum of the individual disturbances. • When waves cross in a point and have the same sign amplitude, they add constructively. Since intensity is proportional to amplitude squared, the resulted intensity is more than the sum of the intensities of individual waves. Constructive Interference
Lecture 21 Purdue University, Physics 220 5 • The net disturbance is the sum of the individual disturbances. • When waves cross in a point and have the opposite sign amplitude, they add destructively. • Since intensity is proportional to amplitude squared, the resulted intensity is less than the sum of the intensities of individual waves. Destructive Interference

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Lecture 21 Purdue University, Physics 220 6 In phase φ =0 Out of phase by φ = π Out of phase by φ =(2/3) π Fully Destructive Destructive Constructive Destructive Interference
Lecture 21 Purdue University, Physics 220 7 Two waves are coherent when their

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Lecture21 - PHYSICS 220 Lecture 21 Waves Textbook Sections...

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