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## Waves Intro

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### Waves Intro Chapter 25 Standing Waves Occurs when two waves traveling in opposite directions in the same medium, with the same amplitude and same frequency Resultant ... – PowerPoint PPT presentation

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Title: Waves Intro

1
Waves Intro
• Chapter 25

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

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

4
Wave Types
• Two main types
• Transverse
• 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

6
Longitudinal Waves
• Motion of the disturbance is parallel to the
direction of the wave propagation
• Example Sound

7
Surface Waves
• Combination of transverse and longitudinal waves
• Example Water

8
Water Waves (surface)
9
Wave Characteristics
• Amplitude, A (m)
• Displacement away from equilibrium point
• Wavelength, ? (m)
• Length of 1 wave cycle
• Period, T (s)
• Amount of time for 1 wave cycle

10
Wave Characteristics (cont)
T (s)
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)
• ? 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
• 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

20
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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.

23
Wave Motion
• Waves propagate in all directions without barriers

24
Wave Fronts
• Line that represents waves that are all in phase,
usually crests

25
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

26
Interference
• Constructive Interference
• When 2 waves interfere with resultant wave having
larger amplitude
• Destructive Interference
• When 2 waves interfere with resultant wave having
smaller amplitude

27
Simulation Examples
• http//www.surendranath.org/Applets/Waves/TWave02/
TW02.html

28
Interference Example
• Two point sources (green dots)
• What do the red dots represent?
• What do the blue dots represent?

29
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

30
Doppler Effect
• Change in frequency due to moving wave source or
observer
• Example
• Example

31
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

32
Sonic Boom
• When moving object exceed the speed of sound, air
builds up into a shock wave

33
Sonic Boom
34
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35
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

36
Nodes and Antinodes
• Nodes
• Points of maximum destructive interference
• Antinodes
• Points of maximum constructive interference

37
Nodes and Antinodes
38
Nodes and Antinodes
39
Video
• How does this work?

40
Resonance
• Natural Frequency
• 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

41
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

42
Harmonics
• Fundamental Frequency(1st Harmonic)
• Lowest frequency possible
• 2nd Harmonic
• 2x frequency of 1st Harmonic (Octave higher)

43
Closed Pipe Harmonics (Lab)
• 1st Harmonic L 1/4?
• ? 4L
• 3rd Harmonic L ¾ ?
• ? 4/3L
• 5th Harmonic L 1 1/4 ?
• ? 4/5L

44
Open Pipe Harmonics
• 1st Harmonic L ½?
• ?2L
• 2nd Harmonic L ?
• 3rd Harmonic L 1 ½ ?
• ?2/3L