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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
  • 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

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
  • YouTube 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
  • Google Tacoma Narrows Bridge

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
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