1. Waves 1
Chapter 25

2. Vocabulary Wave Pulse Medium
Vibratory disturbance that propagates (moves) through a medium
Pulse
Single disturbance
Medium
Material through which a wave propagates

3. Waves
Waves transfer energy from one place to another, not mass

4. Wave Types Two main types Transverse Longitudinal
Motion of the disturbance is perpendicular to the direction of the wave propagation
Longitudinal
Motion of the disturbance is parallel to the direction of the wave propagation

5. Transverse Waves
Motion of the disturbance is perpendicular to the direction of the wave propagation
Example: Light
TRANSVERSE WAVES

6. Longitudinal Waves
Motion of the disturbance is parallel to the direction of the wave propagation
Example: Sound
LONGITUDINAL WAVES

7. Surface Waves Combination of transverse and longitudinal waves
Example: Water

8. Water Waves (surface)

9. Wave Characteristics Amplitude, A (m) Wavelength, λ (m) Period, T (s)
Displacement away from equilibrium point
Wavelength, λ (m)
Length of 1 wave cycle
Period, T (s)
Amount of time for 1 wave cycle

10. Wave Characteristics (cont)
Crest
λ (m) A
T (s)
Trough

11. Wave Characteristics (cont)
Frequency, f (Hz or s-1)
Number of cycles per second
Inverse of period
Speed, v (m/s)
How fast wave is traveling
Related to frequency (period) and wavelength

12. Equations f = frequency (Hz) T = period (s) v = speed (m/s)
λ = wavelength (m)

13. Light Light is also called electromagnetic radiation
Light is a combination of fluctuating electric fields and magnetic fields that are perpendicular to each other

14. Electromagnetic Spectrum

15. Electromagnetic Spectrum
R Radiowave
M Microwave
I Infrared
V Visible
U Ultraviolet
X X-Rays
G Gamma
C Cosmic
Wavelength
Decreases
Frequency
Increases
Energy
Increases

16. Light (cont) Transverse Wave Travels through vacuum
Color is based on frequency
Green Light = 5.6 x 1014 Hz
Speed of light in a vacuum (air also)
c = 3 x 108 m/s

17. Sound Longitudinal Wave Needs a material (medium) to move
Pitch is based on frequency
Concert A = 440 Hz
Speed of Sound in air is dependent on Temp
v = 331 m/s at STP

18. Wave Speed Waves must follow the kinematic equation
The speed of waves depends upon the material that the wave travels through

19. Wave Speed Sound can not travel in a vacuum, light can
Light travels fastest in a vacuum, slower in all other materials
Sound travels faster in more dense materials

21. Phase Difference
Two points are considered “in phase” when they are at the same point in a wave cycle
The amount of “in or out of phase” is measured in degrees

22. Phase Difference Examples
What point is in phase with A?
B and D are how far out of phase?
Name two other points in phase with each other.

24. Wave Motion
Waves propagate in all directions without barriers

25. Wave Fronts
Line that represents waves that are all in phase, usually crests

26. Principle of Superposition
When two waves meet, they combine together briefly, then go their separate ways
Crest + crest = bigger amplitude
Trough + trough = bigger amplitude
Crest + trough = lower amplitude

27. Interference Constructive Interference Destructive Interference
When 2 waves interfere with resultant wave having larger amplitude
Destructive Interference
When 2 waves interfere with resultant wave having smaller amplitude

28. Simulation Examples

29. Interference Example Two point sources (green dots)
What do the red dots represent?
What do the blue dots represent?

30. Sound Beats Interference produced when two sounds interact
Frequency of beats is equal to difference of frequencies of two sounds
Concept used to tune pianos
Demo

32. Standing Waves
Occurs when two waves traveling in opposite directions in the same medium, with the same amplitude and same frequency
Resultant wave appears to be standing still
Demo

33. Nodes and Antinodes Nodes Antinodes
Points of maximum destructive interference
Antinodes
Points of maximum constructive interference

34. Nodes and Antinodes

35. Nodes and Antinodes

36. Doppler Effect
Change in frequency due to moving wave source or observer
Example

37. Doppler Effect
When distance between source and observer is decreasing, frequency increases
Blue Shift
When distance between source and observer is increasing, frequency decreases
Red Shift

38. Sonic Boom
When moving object exceed the speed of sound, air builds up into a shock wave

39. Sonic Boom

41. Video
YouTube Video
How does this work?

42. Resonance Natural Frequency Resonance
Particular frequency that every elastic body will vibrate at if disturbed
Resonance
Vibration of a body at its natural frequency because of the action of a vibrating source of the same frequency

43. Real Life
Microwaves produce waves that have the same frequency as the vibrational frequency of water molecules
UV rays have the same frequency as certain chemicals in human skin, causing sun burns
Google – Tacoma Narrows Bridge

44. Harmonics Fundamental Frequency(1st Harmonic)
Lowest frequency possible
2nd Harmonic
2x frequency of 1st Harmonic (Octave higher)

45. Closed Pipe Harmonics (Lab)
1st Harmonic L = 1/4
 = 4L
3rd Harmonic L = ¾ 
 = 4/3L
5th Harmonic L = 1 1/4 
 = 4/5L

46. Open Pipe Harmonics 1st Harmonic L = ½ =2L 2nd Harmonic L = 
3rd Harmonic L = 1 ½ 
=2/3L