1. Chapter 20 Traveling Waves
The wave model
One-dimensional waves
Sinusoidal Waves
5. Sound and Light
6. Power and Intensity
7. Doppler Effect

2. Stop to think 20. 1. page 605 Stop to think 20. 2
Stop to think 20.1 page 605 Stop to think 20.2 page 607 Stop to think 20.3 page 610 Stop to think 20.4 page 616 Stop to think page 626
Example 20.1 page 604
Example 20.4 page 614
Example 20.6 page 617
Example 20.9 page 621
Example page 624

3. Wave Model
Traveling wave

4. Wave phenomena
A bit of gossip starting in Washington reaches New York [by word of mouth] travels between these two cities. There are two quite different motions involved, that of the rumor, Washington to New York, and that of the persons who spread the rumor. The wind, passing over a field of grain, sets up a wave which spreads out across the whole field. Here again we must distinguish between the motion of the wave and the motion of the separate plants, which undergo only small oscillations… The particles constituting the medium perform only small vibrations, but the whole motion is that of a progressive wave.
The essentially new thing here is that for the first time we consider the motion of something which is not matter, but energy propagated through matter.

5. Two type of wave motion Longitudinal wave: vibration is
parallel to the direction of wave motion
Transverse wave: vibration is perpen-
dicular to the wave motion

6. One-dimensional Waves
Basic variables of wave motion
Wavelength λ: the minimum distance between any two identical points on adjacent waves
Period T: the time required for two identical points of adjacent waves to pass by a point.
Frequency f: the inverse of the period.
Amplitude A: The maximum displacement
Wave speed V: propagating speed. V = λf

7. The speed of waves on strings
If the tension in the string is T, and its mass per unit length is μ (μ =m/L)
The wave speed is :
Ex.20.1
T = mg, μ = kg/m

8. Sinusoidal Waves
Traveling in the positive x-direction

9. P.20.42
What is the wave speed?

10. P.20.41
V=4.0m/s
What is the wavelength?

11. Sound and Light

12. Electromagnetic waves
Electromagnetic wave speed in vacuum:
V = C = 3.00 × 108 m/s
F = V/λ
The index of Refraction:
The frequency of a wave does not change as the wave moves from one medium to another, but λ(mat) = λ(vac)/n

13. Power and Intensity
When a wave impinges on a surface of area A ( the surface is perpendicular to the direction in which the wave is traveling), we define the intensity I : SI units W/m2

14. The Doppler Effect
Doppler effect: the frequency of the sound you hear is changed when the source or observer moves, this is called Doppler effect.

15. An observer O (the cyclist) moves with a speed Vo toward a stationary source S. The observer hears a frequency f ´ that is greater than the source frequency

16. A source S moving with a speed Vs toward a stationary observer A
A source S moving with a speed Vs toward a stationary observer A. Observer A hears an increased frequency
General case:

17. How fast are the police traveling?
A police siren has a frequency of 550 Hz as the police car approaches you, 450 Hz after it has passed you and is receding. How fast are the police traveling?
( we use the speed of sound V = 343m/s )
as police car approaches you
when car has passed you