Lesson 5.4 Homework
Note: Use sped of sound v = 340 ms
1
if it is not given.
1.
The pressure amplitude of a sound wave in air at 0
o
C is 3.0 x 10
3
Pa.
What is the displacement amplitude if the frequency is 100 Hz?
Density of air = 1.29 kg.m
3
.
2.
If the speed of sound in air at 0
o
C is 332 ms
1
, what is the speed of
sound in air at 20
o
C?
3.
The pressure variation in a sound wave is given by
0.0025cos
1700
3
p
x
t
π
π
=

where p is measured in pascals, x in
meters and t in seconds. Determine
(i)
the wavelength of the wave.
(ii)
the frequency of the wave.
(iii)
the wave speed
(iv)
the displacement amplitude of the wave assuming that the
density of the medium is 3.2
×
10
3
kg m
3
.
4.
(i)
What is the intensity level of a sound that has an intensity I =
7.5
×
10
6
W.m
2
?
(ii)
What is the intensity of a sound that has an intensity level of 35
dB?
5.
Two sound waves have equal displacement amplitudes, but one has
twice the frequency of the other. Find the ratio of their pressure
amplitudes. What is the ratio of their intensities?
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 Fall '10
 George
 Physics, Work, Frequency, intensity level, 3 Pa, 6 W, 1.29 kg

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