DHC 161 practice test
Midterm #2 will be given in class on Friday, Feb. 24
a. These problems are representative of those you will see on the midterm. It is not
comprehensive (i.e., not every topic is covered in this practice test).
b. You should bring a calculator to the exam. You may also refer to your worksheets during
c. For open-ended problems, you must clearly show how you arrived at your answer to earn
full credit. Circle or box your final answer. For multiple choice or true/false problems,
explaining your choice makes you eligible for partial credit if your answer is wrong.
Circle the letter of the best answer for each question. (2 points each)
1. The spectrum of a flute that is plugged at the far end (all finger holes closed) contains
a) all the harmonics
b) primarily even harmonics
c) primarily odd harmonics
d) overtones, but not harmonics
e) none of the above
2. A vibrating string or column of air produces a definite pitch because
a) it can vibrate at only one standing wave
b) all the standing waves have the same amplitude
c) all the standing waves have the same number of nodes
d) the standing waves occur at frequencies that follow the harmonic series
e) the standing waves occur at whole number frequencies (e.g. 80 Hz, but not 81.4 Hz).
4. Which of the following frequency ratios corresponds to the largest musical interval (the
largest gap between notes)?
5. Which mass-spring combination will have the lowest natural frequency?
a) largest mass with the stiffest spring
b) smallest mass with the stiffest spring
c) largest mass with the least stiff spring
d) smallest mass with the least stiff spring
e) Natural frequency does not depend on mass or stiffness.
6. If the closed end of a pan pipe is unblocked, the pitch of that pipe will
a) stay the same.
b) be an octave higher.
c) be an octave lower.
d) be a perfect 5 th higher.
e) be a perfect 4 th lower.
7. In which of the following strings will waves travel fastest?
a) Highest tension and largest weight per length.
b) Highest tension and smallest weight per length.
c) Lowest tension and largest weight per length.
d) Lowest tension and smallest weight per length.
e) Both a) and d).
8. A positive pressure pulse (created when a double reed briefly opens) travels down a tube
that is open at the far end. When the pulse reaches the end,
a) it does not come back.
b) it comes back more or less unchanged.
c) it comes back as a negative pulse.
d) it comes back as a sine wave.
9. If you heard only the 5th and 6th harmonics of some harmonic series, which musical
interval would you hear?
a) a perfect fifth
b) a major sixth
c) a minor third
d) a major 11th
10. ______ An object shaken at its resonance frequency is more likely to break if the object
has a lot of damping than if it has little damping.
11. ______ An object needs to be shaken with a large amplitude in order for resonance to
12. ______ If a system is vibrating with constant amplitude, then we know that the rate at
which the source is putting energy into the system equals the rate at which
damping is taking energy out of the system.
13. ______ The response curve of a Helmholtz resonator shows a single peak.
14. ______ The response curve of a metal plate shows several evenly spaced peaks.
Questions 15-19 refer to the simple stringed instrument shown below. The numbers on the
box represent centimeters from the left end of the string. For each of these problems, you
must explain how you got your answer in order to receive full credit.
0 20 40
15. Sketch the standing wave corresponding to the fourth harmonic of this string. Label each
node with a "N" and each antinode with an "A".
16. Based on your sketch, what is the wavelength of the fourth harmonic?
17. If the wave speed in this string is 200 m/s, what is the frequency of the fundamental?
18. After this string is plucked (near the end), how many cm from the end should it be briefly
touched in order to suppress the first three harmonics (but not the fourth)? Explain.
19. If the tension were increased in the string and you repeated the demonstration of touching the
string to suppress the first 3 harmonics, would you touch closer to the left end, right end, or
touch the same place as before?