1. The Doppler Effect PHY238Y Lecture 13 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:
Thanks to dr. Rod Nave for the permission to use the above resource

2. Example (Ear amplifier)
PHY238Y Lecture 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 m.
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. PHY238Y Lecture 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. Attenuation length (mm)
PHY238Y Lecture 13
Attenuation of sound waves in various media
Material
Frequency (Hz)
Attenuation length (mm)
Water 20
105
106
Muscle
4*10-2
Bone
4*10-3
3.5*106
6*10-4

5. PHY238Y Lecture 13 Noise; noise reduction Decrease of sound intensity:
where a is the characteristic dissipation coefficient for a given medium

6. PHY238Y Lecture 13
Sound source is stationary, observer (detector) is moving “into the waves”

7. PHY238Y Lecture 13
Doppler effect for a source at rest (a) and moving (b).
Observer (detector) is at rest.

8. PHY238Y Lecture 13 Both detector (observer) and source move
Speed of sound is v
Speed of the observer is v0
Speed of the source is vs

9. PHY238Y Lecture 13

10. PHY238Y Lecture 13

11. PHY238Y Lecture 13

12. ? Is Doppler effect an illusion? PHY238Y Lecture 13
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 ?