1. Honors Physics Chapter 14
Waves and Sound
Honors Physics
Chapter 14

2. Definition of a wave
A disturbance that propagates from 1 place to another.
Characterized by a large transfer of energy without a large transfer of medium

3. Types of waves
Mechanical waves: require a medium (air, water, ropes) to travel
Electromagnetic waves: do not require a medium to travel (light, radio)
Matter waves: produced by electrons and particles

4. Mechanical Waves
Transverse: the displacement of the individual particles is perpendicular to the direction of propagation.

5. Mechanical Waves
Longitudinal: The displacement of the individual particles is parallel to the direction of propagation.

6. Mechanical Waves
Surface waves: the displacement of individual particles is circular (result of both transverse and longitudinal motion)

7. Waves in motion
Longitudinal and Transverse Wave Motion

8. Properties of waves
Amplitude (A): the maximum displacement from equilibrium position, measured in meters.
Wavelength ( λ): the distance between 2 particles that are in phase with each other, measured in meters.

9. Wave diagram

10. Properties of waves
3. Frequency (f): number of complete waves that pass a point in one second, measured in 1/seconds or Hertz (Hz)
4. Period (T): the time it takes for one complete wave to pass a given point, measured in seconds.

11. Properties of waves
Velocity of propagation (v): horizontal speed of a point on a wave as it propagates, measured in m/s.

12. Relationships/equations
T =1/ f
or f = 1/T
v = f × λ

13. Phase In-phase: when waves are synchronized (crest meets crest)
Out-of-phase: waves are not synchronized
Opposite phase (180º out-of-phase): crest meets trough

14. Reflections
Fixed End:
Explanation
Animation
Open End:
Between different mediums scroll down (What do you notice about the phases? Transmitted? Reflected?)

15. Principle of Superposition
Occurs when two waves travel through the same medium at the same time.
Each wave affects the medium independently.
The displacement of the medium is the algebraic sum of the displacements.
Animation (scroll down)

16. Interference
Constructive: occurs when wave displacements are in the same direction (in-phase)
Destructive: occurs when wave displacement are in different directions (out-of-phase)
animation

17. What is Sound? Longitudinal Mechanical Rarefaction: low air pressure
Compression: high air pressure
module
animation
What is Sound?

18. Speed of sound Depends on… Temperature V air = 331m/s +(0.6 m/s/ºC)*T
Density/kind of medium
Gases <liquids<solids
Chart of speeds

19. Speed of sound

20. Pitch
How we perceive variations in frequency
Audible range 20-20,000 Hz (listen)
Most sensitive to 1,000 to 5,000Hz
Loudness can distort our perception of pitch (listen tape)
module

21. Doppler Effect
Variation in the frequency of sound due to the relative motion of the sound source or the listener.
Animation1
Picture of a sonic boom
Video of sonic boom
Space shuttle breaking sound barrier

22. Doppler Effect Results
As an moving sound source approaches a listener the frequency (pitch) increase.
As a moving sound source passes by a listener the frequency (pitch) decreases.
*Same effect if sound source is stationary and listener is moving.

23. Calculating Frequency change
f’ = f (v ± vR / v± vs)
f’ = new frequency
f = original frequency of source sound
v: velocity of sound
vR: velocity of receiver
vs: velocity of source

24. Loudness
How we perceive variations in amplitude and intensity.
Module
In general, sound waves of higher intensity sound louder but we are not equally sensitive to all frequencies.

25. Sound Intensity
The amount of energy that passes through a given area in a given time.
I=P/A
P=power (watts)
A = area (m2)
I = intensity (W / m2)
Directly proportional to the square of the amplitude.
Inversely proportional to the square of the distance from the source.

26. Relative Intensity
Logarithmic scale used to indicate the intensity level of a sound.
Measured in decibels or dB
β= 10 log (I / Io)
Io =1×10-12 W/m2 (intensity of the faintest sound that can be heard)
I = intensity of sound in W/m2

27. How loud is a decibel?
Threshold of hearing( Io )= 0dB (air pressure 2×10-5 Pa)
Threshold of pain = 120 dB (air pressure = 20 Pa)
We perceive a 10 dB increase as twice as loud.
Every 20 decibels air pressure increases 10 times
Table of sound levels

28. Resonance
Causing the vibration of an object by the influence of another vibrating body.
Must match the natural frequency of vibration of the object
Whole-number multiple of the natural frequency work too.
DEMO (wood blocks)

29. Standing waves
Caused by the interference of reflected waves with incident waves from the source.
Nodes: pts of no displacement
Antinodes: pts of maximum displacement
Animation
applet

30. Vibrating Columns of Air
Column will emit a sound when the air inside achieves resonance.
DEMO (cardboard moose call)
Frequency of vibration depend on
Length of column
Type of column
Open end
Closed end

31. Fundamentals and Harmonics
Fundamental Frequency: lowest frequency of vibration
Harmonics: whole number multiples of the fundamental
Note: the fundamental frequency is the 1st harmonic.
Animation

32. Closed (at one end) pipe
The standing wave created has
Node at closed-end
Antinode at open-end A N

33. Calculations for closed pipe
Fundamental frequency
f1= v /4L (L=length of air column)
Harmonics
fn = nf1 (n=1,3,5,…)
λ =4L/n
Note: only ODD harmonics are produced
Animation

34. Open pipe
The standing wave created has
Antinode at both ends A A

35. Calculations for open pipe
Fundamental frequency
f1= v /2L (L=length of air column)
Harmonics
fn = nf1 (n=1,2,3,…)
λ =2L/n
Note: ALL harmonics are produced
animation

36. Frequency
Light
Sound (listen)
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