Reflection of Sound

Ms.RhodesPhysics CP1

What happens when a sound wave changes

medium or encounters an obstacle?

1. Reflection off obstacle. Bounces back

2. Transmission- travels into new medium (gets absorbed)

3. Diffraction around obstacle

Diffraction

1. Depends on size of obstacle compared to wavelength.

2. Larger wavelengths diffract more than smaller ones.

Diffraction

Lower frequency = longer wavelengths!

Because you know I'm all about that bass,'Bout that bass, no trebleI'm all 'bout that bass, 'bout that bass, no treble”

Diffraction

Travel great distance! Reflect Back!

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

LAW OF REFLECTION

2. Shape of obstacles

1. Dissimilarities of Medium

Reflection depends on…

Reflection#1 Dissimilarity of Mediums

• More dissimilar = more reflected

• Air –concrete = More reflected, less transmitted (absorbed)

• Air – foam = less reflected, more transmitted (absorbed)

REFLECTION

#2 Shape of obstacle

• Parabolic shape focuses sound to one focal point

http://www.nde-ed.org/EducationResources/HighSchool/Sound/reflection.htm

Reflections / shape

• Satellite Discs

• Bull Moose

• Owl – Facial Discs

• Parabolic Microphones (megaphones)

• Hollywood Bowl

In Auditoriums, do you think they use smooth or rough

walls? Why?

•Rough Walls = reflect sound in a variety of directions

LIVELY FULL SOUND

•Smooth Walls = reflect sound in specific direction

LESS LIVELY AND FULL

http://www.nde-ed.org/EducationResources/HighSchool/Sound/reflection.htm

REFLECTION

• REFLECTION LEADS TO TWO PHENOMENONS

»ECHO

»REVERBERATIONS

Reverberation

• Reflection that occurs in a room less than 17 meters wide

• Brain stores sounds for 0.10th of a second• Sound reflected back will reach you in less

than 0.10th of a second• Sound seems prolonged to person

http://www.youtube.com/watch?v=cYMQme4quOE

Reverberations

Examples

• talking in an empty room• honking horn in a tunnel• singing in the shower

Reverberation Times

• Orchestras = 1-2 sec reverb time

• Choral music = 2-5 sec reverb time

• No reverb time = anechoic

ECHOES• Reflection that occurs in an area greater

than 17 meters wide

• Sound reflected back will reach you later than 0.10th of a second

• Sound sounds like a separate and distinct sound from the original

SONAR• SOund Navigation And Ranging

• Measures time to travel to bottom and return

• When depth gets deeper, the time to travel for the sound increases.

• Time variation displayed on display

Bats Echolocation

RADAR

• Radio Detection and Ranging• Sends out high frequency radio pulses,

reflected back as echoes• Radio waves travel at speed of light• Time of reflection depends on objects

distance away.• Time Variation displayed on screen.

You can determine distance, time and speed of sound from echo.

You can determine distance, time and speed of sound from echo.

#1. Time how long it takes to hear echo.

Look up temp on your phone…

Speed of Sound= 332 + 0.6(Temp)

Speed= distance / time

Solve for distance

NOTE: distance to cliff = 1/2distance

Sample Problem

Indiana Jones yells across the cliff to Shorty who is on the other

side and hears his echo 4.0 sec later. It is a warm day of 37

Celsius. How far away is Shorty?

Known Variables Time = 4 seconds

Temp = 37 C

V = 332 + (0.6T)V = 332 + (0.6 * 37)v = 354.2 m/s

Speed = distance/ Time354.2 = distance/ 41416.8 = distance

distance to other side = ½ ddistance to other side = 708.4 m

Solve for Speed of Sound

Solve for distance

Homework:

1.Sound Reflection Math2.Sound Reflection Concept