PH105
ACOUSTICS
All work on this exam must be your own.
Clearly indicate
your final answer for each question.
EXAM #1
No books or notes may be used.
Section 1: Multiple choice. Write the letter of the best answer for each
question in the blank
on the answer sheet provided. Choose only one answer for each question. No
partial credit
will be given for this section.
1)
If the period of a wave is decreased, then
a)
b)
c)
d)
2)
the
the
the
the
amplitude
amplitude
frequency
frequency
of
of
of
of
the
the
the
the
wave
wave
wave
wave
decreases.
increases.
decreases.
increases.
Which of the following frequency ranges is audible to the human ear?
a)
b)
c)
d)
50-100 Hz
500-1000 Hz
5000-10000 Hz
all of the above.
3)
Which of the following properties of sound is most closely associated
with the pitch of
a musical note?
a)
b)
c)
4)
amplitude
frequency
wave velocity
Two tones have the same amplitude.
a)
b)
c)
d)
Which of the following must be true.
The sounds must be equally loud to the ear.
The sounds must have the same pitch.
The sounds must have the same timbre.
None of the above must be true (though they may be true).
5)
When the amplitude of a sound pressure wave is doubled, the sound pressure
level (in
decibels)
a)
b)
c)
d)
6)
is doubled.
is halved.
decreases by 2 dB.
increases by 6 dB.
"This note is higher in pitch than that note" is a statement about
a)
b)
c)
relative pitch.
absolute pitch.
binaural hearing.
7)
Lying on the floor, you will exert
compared to standing on
the floor.
a)
b)
c)
more
less
the same
8)
A mass oscillates on a spring.
equilibrium,
a)
b)
c)
d)
pressure on the floor,
kinetic
kinetic
kinetic
kinetic
energy
energy
energy
energy
is
is
is
is
maximum
minimum
maximum
minimum
As the mass passes through the point of
and
and
and
and
potential
potential
potential
potential
energy
energy
energy
energy
is
is
is
is
maximum.
maximum.
minimum.
minimum.
9)
The difference between the time each of your ears hears a sound can help
you judge
the
of the sound.
a)
b)
c)
direction
pitch
loudness
10)
As the temperature of the air increases, the speed of sound in air
a)
b)
c)
11)
Which of the following is a false statement?
a)
b)
c)
d)
12)
Sound waves are longitudinal waves.
Sound can travel through a vacuum.
Light travels much faster than sound.
Transverse waves in a guitar string are different from sound waves.
The Doppler shift explains
a)
b)
c)
13)
increases.
decreases.
does not change.
why a sound grows quieter as we move away from the source.
why the siren on a police car changes pitch as it races past us.
the phenomenon of beats.
Two tones of 440 Hz and 444 Hz are played.
a)
b)
c)
d)
The beat frequency is
440 Hz.
444 Hz.
442 Hz.
4 Hz.
14)
Which of the following will not affect the fundamental frequency of
vibration of a
string?
a)
b)
c)
d)
changing
changing
changing
changing
the
the
the
the
amplitude of vibration.
tension of the string.
length of the string.
density of the string.
15)
Compared to the velocity of a 400 Hz sound through air, the velocity of a
200 Hz
sound through air is
a)
b)
twice as great
one-half as great
c)
the same
16)
In general, sound travels fastest through
a)
b)
c)
d)
gases.
liquids.
solids.
vacuum.
17)
In a sound wave, at a place where there is a node in the air pressure
wave, the air
molecule displacement
a)
b)
c)
d)
has a node.
has an antinode.
oscillates between node and antinode.
none of the above.
18)
When a sound wave passes from air into water, it changes direction.
phenomenon
is known as
a)
b)
c)
19)
A sound pressure level of 110 decibels would be considered
a)
b)
c)
20)
refraction.
diffraction.
reflection.
very loud.
average for speaking.
very soft.
In damped harmonic motion, the
a)
b)
c)
amplitude
frequency
period
decreases.
This
21)
If the displacement of vibrating particles is perpendicular to the
direction of
propagation of the wave, the wave is said to be
a)
b)
c)
linear.
transverse.
longitudinal.
22)
There are two organ pipes of the same length. One has one end closed,
while the
other has both ends open. The one with a closed end will emit sound of
a)
b)
c)
a higher frequency.
a lower frequency.
the same frequency.
23)
When a stretched wire (fixed at both ends) is vibrating in the second
harmonic, there
is/are
a)
b)
c)
one node.
two nodes.
three nodes.
24)
Two pure tones cause resonance in different positions along the basilar
membrane.
These tones have different
a)
b)
c)
25)
amplitude.
frequency.
timbre.
Overtones have
a)
b)
c)
longer
shorter
the same
wavelengths, compared to the fundamental.
Section 2: Questions.
all answers.
Partial credit will be given for this section.
JUSTIFY
26)
Sketch a graph of pressure vs time for two sound waves that differ only
in pitch.
Sketch a graph of pressure vs time for two sound waves that differ only
in timbre.
27)
Hz.
A mass on a spring is found to oscillate naturally at a frequency of 0.5
This massspring system is then driven by an oscillator. Describe what happens as
the frequency
of the oscillator is varied from 0.2 Hz to 0.8 Hz.
28)
Sketch the first two normal modes of sound pressure in a tube open at one
end, closed
at the other end. If the fundamental mode has a frequency of 440 Hz,
what is the
frequency of the other mode? Is it harmonic?
29)
Nan is in a fire truck rushing toward the scene of a fire. Stan is
standing at the scene
of the fire. There is no wind. Who hears a higher pitch for the fire
truck's siren?
Explain why.
30)
Explain what is meant by a restoring force.
vibrations to occur?
Why is it necessary for
31)
What is the wavelength of a 440 Hz sound in air, if the speed of sound in
air is 340
m/s? Would the wavelength be longer or shorter if the sound were
passing through water? (Justify.)
32)
A wave pulse travels down the length of a wave machine (like the one in
the front of
the lecture hall). The pulse reflects from the end. Describe the
difference you would
notice between a wave machine with the end free to move and a wave
machine with
the end fixed.
33)
Define diffraction.
waves.
How would you demonstrate diffraction of sound
34)
One sound is made up of equal amplitudes of 110 Hz, 220 Hz, and 440 Hz
pure tones.
A second sound is made up of equal amplitudes of 110 Hz, 330 Hz, and 550
Hz pure
tones. In what way(s) are these two sounds the same? In what way(s) are
these two
sounds different? What is the term given to this combining of pure tones
to get a
complex tone?
35)
Two pure tones are played, one at a constant frequency of 550 Hz, the
other has a
variable frequency. Describe all the phenomena you hear as the frequency
of the
second tone is varied gradually from 550 Hz to 1100 Hz.