Ph 111.01
Fall 2008
Supplement on Amplitude, Intensity and Decibels
The discussion of sound intensity in the textbook does not cover the relationship between
the amplitude of the wave and the intensity.
For the problems we will work, we only
need some very basic information.
Suppose that a wave is described by
(
)
2
2
,
cos
y x t
A
x
t
T
π
π
λ
⎛
⎞
=
−
⎜
⎟
⎝
⎠
Here you can think of
y
as representing the displacement due to a wave on a string, or
water waves in the ocean, or pressure waves traveling in air.
In all these cases there will
be a similar wave function for the velocity of whatever is displaced,
(
)
2
2
2
,
sin
v x t
A
x
t
T
T
π
π
π
λ
⎛
⎞
= −
−
⎜
⎟
⎝
⎠
(This is not the speed of the traveling waveform, but the oscillating back and forth of the
string, air molecules, etc.)
The main thing about these two functions is that they are both
proportional to the amplitude
A
.
This means that potential energy, which is generally
proportional to
y
2
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '08
 Staff
 Work, Ratio, Logarithm, 10 pA, 1 Pa, PA.

Click to edit the document details