Transverse Wave

The direction of particle oscillation is perpendicular to the direction of wave propagation.

http://www.cbu.edu/~jvarrian/applets/waves1/lontra_g.htm

Longitudinal Wave

RarefactionCompression

The direction of particle oscillation is parallel to the direction of wave propagation.

http://www.cbu.edu/~jvarrian/applets/waves1/lontra_g.htm

Speed of Propagation

f

Tv

t

dv

Determined by the medium.

Determined by the source.

Example Problem 1

A) What is the wavelength?

B) What is the amplitude?

It takes 5 [s] for the piece of wave shown to pass a given point.

C) What is the period?

D) What is the speed of the wave?

Intensity and Decibels

area

power

time area

energyintensity

Intensity is measured in watts per square meter.

Intensity follows an inverse square law.

The range of intensities that the human ear can detect is too large to deal with linearly, so a logarithmic scale is used. This scale is known as the decibel scale.

0

log10level decibelI

I

Source IntensityIntensity

Level# of Times

Greater Than TOH

Threshold of Hearing (TOH) 1*10-12 W/m2 0 dB 100

Rustling Leaves 1*10-11 W/m2 10 dB 101

Whisper 1*10-10 W/m2 20 dB 102

Normal Conversation 1*10-6 W/m2 60 dB 106

Busy Street Traffic 1*10-5 W/m2 70 dB 107

Vacuum Cleaner 1*10-4 W/m2 80 dB 108

Large Orchestra 6.3*10-3 W/m2 98 dB 109.8

Walkman at Maximum Level 1*10-2 W/m2 100 dB 1010

Front Rows of Rock Concert 1*10-1 W/m2 110 dB 1011

Threshold of Pain 1*101 W/m2 130 dB 1013

Military Jet Takeoff 1*102 W/m2 140 dB 1014

Instant Perforation of Eardrum 1*104 W/m2 160 dB 1016

Audible Range

• In addition to the range of sound intensities that are detectable by the human ear, there is also a range of frequencies.

• Human beings can typically detect frequencies between 20 [Hz] and 20,000 [Hz]. This is known as the audible range.

• The frequencies that are detectable by the human ear change with age. For example, younger people are able to detect higher frequencies than older people.

Example Problem 2

• A point 2 [m] from a speaker experiences a sound intensity level of 100 [dB]. What is the sound intensity level at a point 5 [m] from the speaker?

Boundary Behavior

• Three things occur when a wave is incident on the boundary between two media:– Part of the wave is reflected (it stays in the

original medium)– Part of the wave is transmitted (it passes

through to the new medium)– Part of the wave is absorbed (some of the

energy is converted to internal energy of particles at the boundary)

Conservation of Energy (yet again)

absorbeddtransmittereflectedincident EEEE

ReflectionLow density to high density

High density to low density

The pulse is inverted.

This corresponds to a phase shift of π radians.

The pulse is not inverted.

This corresponds to a phase shift of 0 radians.

“Low to high, pi. High to low, no.”

The angle of incidence is equal to the angle of reflection.

Refraction

When a wave travels from one medium to another, it experiences a change in speed.

This change in speed results in a change in direction. This is known as refraction.

Doppler EffectThe source is stationary.

The wavefronts have the same spacing for both observer A and observer B.

Both observer A and observer B detect the same frequency, which is the actual frequency being produced.

The source is moving at a speed less than the speed of the wave.

The wavefronts appear closer together to observer B than they do to observer A.

Observer B detects a higher apparent frequency.

Observer A detects a lower apparent frequency.

The source is moving at a speed equal to the speed of the wave.

The wavefronts stack up on one another in the direction that the source is traveling.

For sound, this buildup of pressure is known as the “sound barrier”.

The source is moving at a speed faster than the speed of the wave.

The source is outrunning the wavefronts it produces.

The cone shaped area of very high pressure is known as a “shock”.