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PHY238Y Lecture 13

PHY238Y Lecture 13. The Doppler Effect References: Halliday, Resnick, Walker: Fundamentals of Physics, 6 th ed., Wiley 2003, Chapter 18 (18.8) Hallett et al.: Physics for the life sciences, 4 th ed., 2003, Ch.2 (2.7) Some of the pictures were taken from Hyper Physics:

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PHY238Y Lecture 13

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  1. PHY238YLecture 13 The Doppler Effect References: Halliday, Resnick, Walker: Fundamentals of Physics, 6th ed., Wiley 2003, Chapter 18 (18.8) Hallett et al.: Physics for the life sciences, 4th ed., 2003, Ch.2 (2.7) Some of the pictures were taken from Hyper Physics: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/soucon.html#soucon Thanks to dr. Rod Nave for the permission to use the above resource

  2. PHY238YLecture 13 • Hearing: pressure in the cochlear liquid vs. pressure on the eardrum (does human ear really amplifies sound?) • Example (Ear amplifier) 1) Calculate the maximum net force on an eardrum due to a sound wave having a maximum pressure of 2* 10-3 N/m2, if the diameter of the eardrum is 0.0085m. 2) Assuming the mechanical advantage of the hammer, anvil and stirrup is 2, calculate the pressure created on the oval window (Ao = 0.03cm2) 3) Assuming the acoustic impedance of air Zair = 416 N*s/m3; and water Zwater = 1.48*106 N*s/m3, calculate the relative transmission of the oval window to sound waves (stransmitted/sincident).

  3. PHY238YLecture 13 • Absorption of sound: sound waves produce molecular motion in the material they propagate; • Friction reduces intensity by energy dissipation. • Inside a medium: • The attenuation length x0 depends strongly on: frequency and the type of medium involved.

  4. PHY238YLecture 13 Attenuation of sound waves in various media

  5. PHY238YLecture 13 • Noise; noise reduction • Decrease of sound intensity: where a is the characteristic dissipation coefficient for a given medium

  6. PHY238YLecture 13 Sound source is stationary, observer (detector) is moving “into the waves”

  7. PHY238YLecture 13 Doppler effect for a source at rest (a) and moving (b). Observer (detector) is at rest.

  8. PHY238YLecture 13 • Both detector (observer) and source move • Speed of sound is v • Speed of the observer is v0 • Speed of the source is vs

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  12. PHY238YLecture 13 • Is Doppler effect an illusion? J.G. Neuhoff, M.K. McBeath: Am. J. Phys., Vol.65(7), 1997 found out that: • Perceptual processing of frequency and intensity interact; • Judgments about magnitude and direction of pitch change are influenced by changes in loudness; • The intensity of a Doppler-shifted tone rises as the source approaches; loudness changes influence pitch change, so pitch is also perceived to rise ?

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