Sound
Waves
Intensity
:
where
I =
the intensity of the sound
Io =
the minimum detectable intensity of sound ( Io = 10-12
W m-2 )
The
bel (B) is the unit of
intensity level.
In
practice, the bel is too large, we define a new unit called decibel
(dB)
1 B = 10 dB
∴
Phons:
The
source H whose loudness is required to measure is placed near
the
standard source of 1 kHz.If
the intensity level of the standard
source
is n dB above threshold value, then the loudness of the
source
H is said to be n phons.
Doppler
Effect in sound :
Shock
waves
: 
Doppler
effect in light ( or electromagnetic waves)
:
(1)
Source and observer
approaching
fo
= (1 + v/c) f
(2)
Source and observer
separating
fo
= (1 - v/c) f
