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Superposition and Interference

Superposition and Interference. Review of Superposition. Two sound waves arriving at the same point P:. Pressure fluctuations. +. Pressure fluctuations. Resulting pressure fluctuation at P. Signal at P. p(t). time t. Signal at P: constructive interference. p(t). time t.

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Superposition and Interference

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  1. Superposition and Interference

  2. Review of Superposition • Two sound waves arriving at the same point P: Pressure fluctuations + Pressure fluctuations Resulting pressure fluctuation at P

  3. Signal at P p(t) time t

  4. Signal at P: constructive interference p(t) time t The sound wave is enhanced Δt= 2τ Δt= 0 Δt= -τ When will this happen? Δt=n*τ n=…-2,-1,0,1,2,… any whole number

  5. Signal at P: destructive interference p(t) time t The sound wave is canceled out. Δt=-1/2*τ Δt=-τ-1/2*τ Δt=+1/2*τ When will this happen? Δt=(n+1/2)*τ n=…-2,-1,0,1,2,… any whole number

  6. Superposition • Constructive interference: The wave is enhanced if • Destructive interference: The wave is canceled if

  7. In space: Lines of constructive interference ΔL=nλ (maxima and minima arrive at same time at points on these lines)

  8. In space: Lines of destructive interference ΔL=(n+1/2)λ (maxima of one wave and minima of the other arrive at same time at points on these lines)

  9. Path length diffence How many rays are there coming from a point source? ΔL=1.5λ ΔL=0 Two rays traveling parallel.

  10. Better… • Use overhead projector for demonstration

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