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Wave PhenomenaWave Phenomena
Characteristics of Waves
Characteristics of Waves
What is a wave?What is a wave?A wave is a vibratory
disturbance through a material (medium) or space
Waves transfer ENERGY without transferring mass
A wave is a vibratory disturbance through a material (medium) or space
Waves transfer ENERGY without transferring mass
Classifying Waves1. Electromagnetic
waves
Classifying Waves1. Electromagnetic
wavesNo medium requiredTravel at the speed of light c = 3 x 108 m/sExamples: visible light, x-rays,
infraredReference Table: Electromagnetic
spectrum
No medium requiredTravel at the speed of light c = 3 x 108 m/sExamples: visible light, x-rays,
infraredReference Table: Electromagnetic
spectrum
2. Mechanical Waves2. Mechanical Waves
A. Longitudinal waves - vibrate parallel to wave motion
Examples - sound, seismic s-waves
A. Longitudinal waves - vibrate parallel to wave motion
Examples - sound, seismic s-waves
Require a medium ex. Sound, water, waves in springs
B. Transverse waves - vibrate perpendicular to wave motionExamples: light, seismic p-waves, water
Transverse or longitudinal?
Longitudinal
Transverse
What is a pulse? How can we describe its motion?
What is a pulse? How can we describe its motion?
Pulse
Periodic wave
A pulse is a single vibration moving at constant speed
ImportantImportant
Speed of a wave or pulse doesn’t change unless the characteristics of the medium change
Speed of a wave or pulse doesn’t change unless the characteristics of the medium change
Periodic WavesPeriodic Waves
Sketch:Sketch:
frequency (f):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:
wavelength (): wavelength ():
distance between two points in phase
units: meters
phase:phase:
points on wave having the same displacement from rest position AND moving in the same direction (up or down only) are in 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
speed:
units: m/s
amplitude:
maximum displacement of a particle from rest position
Examples:Examples:
L = 3mv = 12 m/s
f T
6 m
3 m
2 m
v = f T=1/f
2 Hz
4 Hz
6 Hz
.5 s
.25 s
.17 s
Relationship between T, f and
Relationship between T, f and
As frequency increases (at constant velocity), what happens to wavelength?
decreases
As frequency increases, what happens to period?
decreases
As frequency increases (at constant velocity), what happens to wavelength?
decreases
As frequency increases, what happens to period?
decreases
Doppler EffectDoppler EffectChange in “apparent” frequency
caused by relative motion between a source and an observer
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
Examples: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
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
Point source Line source
What is a wave front?
Adjacent points on a wave that are in phase with each other
Wave fronts for a moving object:Wave fronts for a moving object:
Point source - stationary Point source -moving
What happens to a wave when a new medium is encountered?What happens to a wave when a new medium is encountered?Frequency from the source is
constantSince v = f, if velocity changes,
then wavelength changes
Wave can be reflected, transmitted through a new medium, or absorbed by the new medium
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
How can we describe wave interference?
How can we describe wave interference?
Two or more waves pass through the same region - original wave is unchanged
Two or more waves pass through the same region - original wave is unchanged
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)
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)
Constructive or Destructive?
Destructive - 180° out of phase
Constructive or Destructive?
Constructive - 0° or 360° (in phase)
Constructive or Destructive?
Constructive or Destructive?
Both constructive and destructive
Law of SuperpositionLaw of SuperpositionResultant displacement is the
algebraic sum of the displacements due to the individual waves
Resultant displacement is the algebraic sum of the displacements due to the individual waves
The red wave is the resultant wave.
What will the resultant wave look like?
What will the resultant wave look like?
What are standing waves
What are standing waves
Two waves of the same frequency and amplitude moving in opposite directions
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
Sketches:
Sketches: L
2L
L
L/2
2/3 L
/2
3/2
2How are the number of nodes related to the number of antinodes?
N = A + 1