A synthesizer is a keyboard instrument that can be made to sound like a flute, a trumpet, a piano—or any other musical instrument. Pressing a key sets the fundamental frequency of the note that is produced. Other settings that the player can adjust change the sound quality of the synthesizer without altering the fundamental frequency. How is this change accomplished? What is being adjusted?

You are listening to music from a loudspeaker. Then a second speaker is turned on. Is it possible that the music you now hear is quieter than it was with only the first speaker playing? Explain.

The fundamental frequency of a stretched string is 150 Hz. What are the frequencies of (a) the second harmonic and (b) the third harmonic?

A guitar string with a linear density of 2.0 g/m is stretched between supports that are 60 cm apart. The string is observed to form a standing wave with three antinodes when driven at a frequency of 420 Hz. What are (a) the frequency of the fifth harmonic of this string and (b) the tension in the string?

What was the approximate length of the tube?
A. $0.35 \mathrm{~m}$
B. $0.70 \mathrm{~m}$
C. $1.4 \mathrm{~m}$
D. $2.8 \mathrm{~m}$

Sopranos can sing notes at very high frequencies---over 1000 Hz. When the sing such high notes, it can be difficult to understand the words they are singing. Use the concepts of harmonics and formats to explain this.

A wave pulse travels along at string at a speed of 200 cm/s. What will be the speed if: a. The string's tension is doubled? b. The string's mass is quadrupled (but its length is unchanged)? c. The string's length is quadrupled (but its mass is unchanged)? d. The string's mass and length are both quadrupled? Note that parts a - d are independent and refer to changes made to the original string.

A laser beam has intensity $I _ { 0 }$. a. What is the tensity, in terms of $I _ { 0 }$, if a lens focuses the laser beam to 1/10 its initial diameter? b. What is the intensity, in terms of $I _ { 0 }$, if a lens defocuses the laser beam to 10 times its initial diameter?

As we discussed earlier shows frequency spectra of the same note played on a flute (modeled as an open-open tube) and on a clarinet (a closed-open tube). Which figure corresponds to the flute, and which to the clarinet? Explain.

Some bat species have auditory systems that work best over a narrow range of frequencies. To account for this, the bats adjust the sound frequencies they emit so that the returning, Doppler-shifted sound pulse is in the correct frequency range. As a bat increases its forward speed, should it increase or decrease the frequency of the emitted pulses to compensate?

The G string on a guitar is $59 \mathrm{~cm}$ long and has a fundamental frequency of $196 \mathrm{~Hz}$. A guitarist can play different notes by pushing the string against various frets, which changes the string's length. The first fret from the neck gives $A b(207.65 \mathrm{~Hz})$; the second fret gives A (220 Hz). How far apart are the first and second frets?

What can you say about the reflection of sound waves at the ends of a tube?
A. Sound waves are inverted when reflected from both open and closed tube ends.
B. Sound waves are inverted when reflected from a closed-end, not inverted when reflected from an open end.
C. Sound waves are inverted when reflected from an open end, not inverted when reflected from a closed end.
D. Sound waves are not inverted when reflected from either open or closed tube ends.

When you speak after breathing helium, in which the speed of sound is much greater than in air, you voice sounds quite different. The frequencies emitted by your vocal cords do not change since they are determined by the mass and tension of your vocal cords. So what does change when your vocal tract is filled with helium rather than air?

A sun-like star is barely visible to naked-eye observers on earth when it is a distance of $7.0$ light years, or $6.6 \times 10^{16} \mathrm{~m}$, away. The sun emits a power of $3.8 \times 10^{26} \mathrm{~W}$. Using this information, at what distance would a candle that emits a power of $0.20 \mathrm{~W}$ just be visible?