Upload
shoaib-ahmed-siddique
View
240
Download
0
Embed Size (px)
Citation preview
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
1/18
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
2/18
Sound
Sound is a longitudinal mechanicalwave.
Compressions(High Pressure)
Rarefactions(Low Pressure)
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
3/18
Speed of Sound
Depends on the medium.
The more elastic the medium thefaster sound will travel through it.
Speed in metals>speed inwater>speed in air
Sound cant travel throughvacuum.
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
4/18
Speed of Sound in Air
v = 331 + 0.6 T ( in meters/sec)
T is the temperature in 0C.In higher humidity, sound will travelfaster.
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
5/18
Properties of Sound
Reflection (Echo)Refraction
InterferenceDiffraction
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
6/18
Pitch: the frequency of asound wave.
Musical notes have a given pitch.
The note C has a frequency of327Hz.
When two notes differ by a ratio of2:1 they are one octave apart.
What would be the next higher C?
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
7/18
Bow (Shock) Waves
When the speed of a moving soundsource is greater than the speed of thewave, a pressure ridge builds similar
to the wave created by the bow of aship.
physlet animation
http://online.cctt.org/physicslab/content/applets/doppler/Doppler.htmlhttp://online.cctt.org/physicslab/content/applets/doppler/Doppler.htmlhttp://online.cctt.org/physicslab/content/applets/doppler/Doppler.html8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
8/18
Sonic Boom
When the pressure ridge of a bowwave of a jet passes over an observeron the ground, the observerexperiences a sonic boom.
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
9/18
Doppler Effect
The change in a wave's perceivedfrequency due to the motion of either thesound source or the observer.
It is applicable to any type of wave.
Austrian physicist Christian Doppler (1803-1853).train sound clip
Simulationsphyslet animationhttp://www.walter-fendt.de/ph14e/dopplereff.htm
http://online.cctt.org/physicslab/content/Phy1/lessonnotes/waves/TrainDoppler.auhttp://online.cctt.org/physicslab/content/applets/doppler/Doppler.htmlhttp://www.walter-fendt.de/ph14e/dopplereff.htmhttp://www.walter-fendt.de/ph14e/dopplereff.htmhttp://www.walter-fendt.de/ph14e/dopplereff.htmhttp://www.walter-fendt.de/ph14e/dopplereff.htmhttp://online.cctt.org/physicslab/content/applets/doppler/Doppler.htmlhttp://online.cctt.org/physicslab/content/applets/doppler/Doppler.htmlhttp://online.cctt.org/physicslab/content/Phy1/lessonnotes/waves/TrainDoppler.au8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
10/18
The Doppler Effect
http://www.physicsclassroom.com/Class/sound/u11l3b.cfm
http://www.physicsclassroom.com/Class/sound/u11l3b.cfmhttp://www.physicsclassroom.com/Class/sound/u11l3b.cfm8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
11/18
Doppler EffectDetected Frequency, (f D)
f D = f ( v vo )vvsf : frequency of source
v : speed of sound
vo : speed of observer(+)when observer moving towards
source
vs
: speed of source(-)when source is moving towards
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
12/18
Example 1
An ambulance is approaching astationary observer.
The siren of the ambulance emits a
frequency of 480Hz and the speedof the ambulance is50km/h(=13.88m/s).
What frequency will the stationaryobserver hear when the ambulanceis approaching? Assume T=20 oC.
Answer: f d = 500Hz
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
13/18
Sound Intensity (I)
I = (Power transmitted by the Wave)/Area
Threshold of human hearing:
Io =1 x 10 -12 Watts/m 2
Threshold of Pain:IP = 1 Watts/m 2
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
14/18
Sound (Intensity) Level
A measure of our perception of theloudness of the sound.
Unit: decibel(dB)
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
15/18
Sound (Intensity) Level,(decibel)
b= 1 log I , unit for b is dB ( decibel )I0
The decibel compares the sound intensity (I),to I o (1 x 10 -12 Watts/m 2) ,
the threshold of human hearing.
Remember: log(10 x )= x
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
16/18
Examples of Sound IntensityLevels
jet plane taking off 140 dBair raid siren 125 dBthreshold of pain 120 dBloud rock music 115 dBear damage starts 85 dBbusy traffic 70 dBnormal conversation 60 dBquiet library 40 dBsoft whisper 20 dBthreshold of human hearing 0 dB
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
17/18
Example 2
What is the sound level (decibel) ofa sound of 10 -4 W/m 2 intensity ?
Answer: 80dB
8/13/2019 1 Sound, Pitch, Loudness, Doppler Effect
18/18
Example 3
How many times louder is a quiet librarysound (40 dB) compared to a soft whisper(20 dB)?
Hint 1: Property of logs:log(A/B) = logA logB
Hint 2: Take the difference in dB and thenfind
(I2 /I1)