PHY 206 Lecture Notes - Lecture 6: Infrasound
30 Jun 2018
School
Department
Course
Professor
Sound
Characteristicsofsounde
can't travel intheabsence of
matter
speeddependson material
gelasticmodulus
Loudnessy 4intensity insoundwaves W
mz
energy per
time
unit
Pitch's measured
byfrequency 300M a600mih
lowfrequency lowpitch
audibleranget 20Hz 20,000
Hz
Ht cycleper
second
ultrasonicfrequencies above 20,000Ha
infrasonic frequencies below audiblerange 420
He
1mi in l3km
1300M
speed ofsound in air increaseof
speed per C
it 331 t0.60T mIs
1miler1609M
error of 5second Rule
p09
m15
4X100
wave
Mathemalicyrepresentalingudindwave 9
K21
DAsm ka wt Ymsin ex wt X
bwztif
wave Be AI
displacement
PressurewareDerivation
changeinvolume fVolume decreases if tho
AP BAvg duetoDP pressure isincreased
Consider alayeroffluid through
which thewavepasses
het 11 5Ax Ax thickness
DV SAD DD change in thickness
sarea
AP BSDI takelimitas Axto
sDX
DP B2
amplitude
DP BAK cos Kt wt
BAK pressure amplitude Bpa
maximum and minimum amounts bywhribpressurevaries
from normal ambientpressure
AP iDPmcos Kx wt vJB
F
APm BAK
Epriffkraf dem enpraf
s
w
Aspry
PxtPmsin Ckx wt Twp
displacement
Pm Bk Sm 2npvsmf
2tY helm
very
loudsound Pm 30Pa 105Pa
zoltz 0.8mmCdisp
20kHz 0.8mm
IntensityofsoundiDecibelse
his based on wave intensity
intensity AIX rt
amplitude
Lowerlimit
sound level a
20 Decibel dB Ibet thresholdofhearing 1our Mm
Bsoundlevel
12
Iintensity Ioi 10
Bel0logIEo
aptTogEr5Dpe20logCrrtfI.Eiio.a O
Intensity Ii IA e4
distance fICI 102 104
we Ioli
surface
Area
ofsphere 2
Boo Bi 1010945 dB 40dB 10
Pious B40dB e140 40 i100dB
Fif IIo
Daeubel
Bi blog Eto lologll 0dB
I17090
0
Example Awave
has asound levelof60dB
intensity
B10101 Io 10 0II110 m10 01106
Hi
Amen pi 106g'E
