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Unformatted text preview: The Physics of Light & Sound
PRACTICE PROBLEMS
GENERAL SCIENCE 121 SUMMER 2011 1. A string ﬁxed at both ends has a length of 4 m has a wave speed of 10 m/s. Compute the
frequency of the 4th harmonic. ANSWER: 5 Hz
2. The fundamental frequency of a stretched string ﬁxed at both ends is 238 Hz. If the length of the
string doubled but the tension and mass per unit length did not change, what would be the new
fundamental frequency? ANSWER: 119 Hz
3. A closedopen tube has a length of 3.9 m and a sound speed of 348 m/s. Compute the frequency
of the 3rd harmonic. ANSWER: 67 Hz
4. An openopen tube has a length of 3.9 m and a sound speed of 345 m/s. Compute the frequency
of the 5th harmonic. ANSWER 221 Hz
5. Notes of frequency ratio 2 to 3 so that harmonics of 2:3 or 4:6 etc. form is:
A) a perfect fourthSean T Scully  GSCI121_3_4_SP10
B) a perfect ﬁfth Homework #6 5 C) a minor third A 5 m cable ( mass/length of 0.0
ceiling. At the end of the cable,
A standing wave is produced on a stretched string
produce tension in the cable. W
A standing wave is ﬁxed at on a stretched as illustrated both ends as How
produced both ends string ﬁxed at below.
illustrated below. aHow
mental frequency of a standing wa
many nodes and represent?
many nodes and which harmonic does itwhich harmonic does it represent? D) an octave
6. Tries 0/10 Answer
for Part:
0 ANSWER: 11 nodes 9 nodes and the 8th harmonic
A. and the 10th harmonic
B. 1 nodes that harmonics of 1:2
7. Notes of frequency ratio 11 to 2 soand the 10th harmonic or 2:4 etc. form is: A) a minor third C. 11 nodes and the 11th harmonic
D. 9 nodes and the 9th harmonic B) a perfect ﬁfth
C) an octave Tries 0/10 Answer A ﬂute (openopen) is played
362 hz. The length of the air
the speed (in m/s!) of the wav
Tries 0/10 Answer
for Part:
0 • false
• true
0
We wish to design an instrument • false
that is constructed of an openclosed tube. The instrument
• false
needs to produce a note of 1280 hz frequency with the 5th harmonic. What would be the length D) a perfect fourth for Part:
8. of the tube (sound speed = 345 m/s)? ANSWER: 0.34 m Summer 2011 Notes of frequency ratio 3 to 4 so that harmonics of 3:4 or
6:8 etc. form is:
A. a minor third
B. a perfect ﬁfth
C. an octave
1
Practice Problems
D. a perfect fourth Tries 0/10 • 4.6957427527
[4.46095561
4.930529890
Sig 0  15 • 564.72
[536.484
592.956]
Sig 0  15 9. A 5 m cable ( mass/length of 0.04 kg/m) is hung from the ceiling. At the end of the cable, a 9 kg
mass is attached to produce a tension in the cable. What would be the fundamental frequency of a
standing wave produced in this cable? ANSWER: 4.7 Hz
10. A ﬂute (openopen) is played with a ﬁrst harmonic of 362 hz. The length of the air column is 78
cm. Find the speed of the wave resonating in the ﬂute. ANSWER: 565 m/s
11. Sketch the ﬁrst 5 harmonics for openopen, closedopen, and a Kundt tube. Label the nodes and
antinodes. Determine the frequencies if the sound speed is 345 m/s and the length of each tube
is 0.5 m. ANSWER: Kundt and openopen  345, 690, 1035, 1380, and 1725 Hz
(ﬁrst second third fourth and ﬁfth harmonics). Closedopen  172.5, 517.5,
862.5, 1207.5, and 1552.5 Hz (ﬁrst, third, ﬁfth, seventh, and ninth harmonics).
12. Write down the electromagnetic spectrum in order of longest wavelength to shortest, highest
frequency to lowest, lowest energy to highest ANSWER:
RadioIROpticalUVX RayGamma Ray
Gamma RayX RayUVOPticalIRRadio
RadioIROpticalUVX RayGamma Ray
13. Roemer ﬁrst measured the speed of light by:
A) Using an array of mirrors and a high powered light source
B) Bouncing radio waves off of the Moon whose distance was known
C) Spinning a gear while passing light through the cerated edge to a distant mirror
D) Timing the difference in the period of Io (Jupiter's Moon) when the Earth was in two different
locations in its orbit.
14. While looking through a telescope, you observe the Andromeda Galaxy which is 2.5 million light
years away. Which of the following statements is correct?
A) We are seeing Andromeda as it was two and a half million years ago
B) There is not enough information to determine anything about "when" we see Andromeda
C) We see Andromeda as it was 8 minutes ago
D) We see Andromeda as it is today
15. Jupiter is 778,330,000 km from the Sun. How long (in hours) does it take light to travel from the
Sun to Jupiter? ANSWER: 0.72 hours Summer 2011 2 Practice Problems ...
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 Spring '08
 Niculescu,M

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