# Wave Phenomena - PowerPoint PPT Presentation

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## Wave Phenomena

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### Wave Phenomena Characteristics of Waves * * * What is a wave? A wave is a vibratory disturbance through a material (medium) or space Waves transfer ENERGY without ... – PowerPoint PPT presentation

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Title: Wave Phenomena

1
Wave Phenomena
• Characteristics of Waves

2
What is a wave?
• A wave is a vibratory disturbance through a
material (medium) or space
• Waves transfer ENERGY without transferring mass

3
Classifying Waves1. Electromagnetic waves
• No medium required
• Travel at the speed of light
• c 3 x 108 m/s
• Examples visible light, x-rays, infrared
• Reference Table Electromagnetic spectrum

4
2. Mechanical Waves
Require a medium ex. Sound, water, waves in
springs
• A. Longitudinal waves - vibrate parallel to wave
motion
• Examples - sound, seismic s-waves
• B. Transverse waves - vibrate perpendicular to
wave motion
• Examples light, seismic p-waves, water

5
Transverse or longitudinal?
Longitudinal
Transverse
6
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7
• What is a pulse? How can we describe its motion?

A pulse is a single vibration moving at constant
speed
Pulse Periodic wave
8
Important
• Speed of a wave or pulse doesnt change unless
the characteristics of the medium change

9
Periodic Waves
• Sketch

10
• frequency (f)

number of vibrations per unit time units hertz
(1 hertz 1 cycle per second)
period (T)
time required for 1 vibration units
seconds equation
11
• wavelength (?)

distance between two points in phase units meters
12
phase
• points on wave having the same displacement from
rest position AND moving in the same direction
(up or down only) are in phase

Examples A E I, B F, C G, D H
13
speed
?
?
units m/s
14
amplitude
maximum displacement of a particle from rest
position
15
• Examples

? f T

6 m
2 Hz
.5 s
3 m
4 Hz
.25 s
2 m
.17 s
6 Hz
L 3m v 12 m/s
T1/f
v f ?
16
Relationship between T, f and ?
• As frequency increases (at constant velocity),
what happens to wavelength?
• decreases
• As frequency increases, what happens to period?
• decreases

17
Doppler Effect
• Change in apparent frequency caused by
relative motion between a source and an observer

Object moving toward you shorter ? higher f
Object moving away from you longer ? lower f
18
Examples
• 1. Sound - train whistle - higher pitch as it
moves toward you, lower pitch as it moves away.
• 2. Light - Red Shift Evidence of Big Bang
Theory - as universe expands, stars move away,
larger wavelength and smaller frequency - shift
toward red end of spectrum

19
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20
What is a wave front?
Adjacent points on a wave that are in phase with
each other
Point source Line source
21
• Wave fronts for a moving object

Point source - stationary
Point source -moving
22
What happens to a wave when a new medium is
encountered?
• Frequency from the source is constant
• Since v f?, if velocity changes, then
wavelength changes
• Wave can be reflected, transmitted through a new
medium, or absorbed by the new medium

23
How can we describe wave interference?
• Two or more waves pass through the same region -
original wave is unchanged

24
• Constructive interference- two crests meet, or
two troughs meet
• Maximum when phase difference is 0 or 360 (360
is a whole wave)
• Destructive interference - crest meets trough
• Maximum when phase difference is 180 (180 is
half of a wave)

25
Constructive or Destructive?
Destructive - 180 out of phase
26
Constructive or Destructive?
Constructive - 0 or 360 (in phase)
27
Constructive or Destructive?
Both constructive and destructive
28
Law of Superposition
• Resultant displacement is the algebraic sum of
the displacements due to the individual waves

29
The red wave is the resultant wave.
30
• What will the resultant wave look like?

31
What are standing waves
• Two waves of the same frequency and amplitude
moving in opposite directions

Nodes - points that appear fixed Antinodes
(modes) - points of maximum amplitude above and
below rest position
32
Sketches
? L

2L
?/2
L
?
2/3 L
3/2 ?
L/2
2?
How are the number of nodes related to the number
of antinodes?
N A 1