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Interference and Doppler

Interference and Doppler. Questions? Interference in Space Interference in Time (Beats) Doppler Shift Source moving Observer moving Examples Both moving. Interference in Space. Two loudspeakers Example 12-12 FM car radio AM car radio (cellphone) Noise-cancelling headphones.

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Interference and Doppler

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  1. Interference and Doppler • Questions? • Interference in Space • Interference in Time (Beats) • Doppler Shift • Source moving • Observer moving • Examples • Both moving

  2. Interference in Space • Two loudspeakers • Example 12-12 • FM car radio • AM car radio • (cellphone) • Noise-cancelling headphones

  3. Interference in Time • Combine 2 waves slightly different frequency Y = A cosω1t + A cosω2t • Use trig identity to get sum and difference • Result: You get a difference frequency called “beats” • Figure 12-18 combine 50 and 60 Hz waves • Sound animation • Beats animation • Example 12-13

  4. Doppler Shift (Source) • Wavelength modified during wave creation • Source moving toward observer compresses wavelength • But the period is related to velocity and wavelength in still air • And the frequency you hear passing your ear

  5. Doppler Shift (Observer) • Frequency modified during wave passing your ear • Observer moving toward source increases frequency • Summary

  6. Doppler Examples • Example 12-14 • Example 12-15 • Doppler animation • “Doppler weather radar” • “Red Shift” • Problem 54 (Bat) • Problem 55 (Tubas) • Problem 56 (Blood flow) • f’ = 3.499955 Hz • f’’ = 3.499910 Hz • Δf = 90 Hz

  7. Nat’s Adventure • Basic history • 2005 - “you have a heart murmur” (yikes!) • 2008 - Getting worse (mother history) • 2009 - Bicuspid aortic valve, area 0.7 cm2 (should be 3.0 cm2) • June 2010 - All fixed! Back to biking, hiking, skiing (m-o-o-o!) • Ultrasound diagnosis • Valve area from pressure difference • Pressure difference from velocity difference (Bernoulli) • Velocity difference from Ultrasound (Doppler Shift) Just like chapter 12, problem 56! High pressure Low pressure flow

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