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