Reflection of Sound Ms.Rhodes Physics 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!

Diffraction Travel great distance!Reflect Back!

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

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

REFLECTION REFLECTION LEADS TO TWO PHENOMENONS »ECHO »REVERBERATIONS

Reverberation Reflection that occurs in a room less than 17 meters wide Brain stores sounds for 0.10 th of a second Sound reflected back will reach you in less than 0.10 th of a second Sound seems prolonged to person

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 0.10 th 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= (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 = (0.6T) V = (0.6 * 37) v = m/s Speed = distance/ Time = distance/ = distance distance to other side = ½ d distance to other side = m Solve for Speed of Sound Solve for distance

Homework: 1.Sound Reflection Math 2.Sound Reflection Concept