READING QUIZ Sound waves can travel in air 1.but not in outer space 2.but not in steel. 3.but not in water.

READING QUIZ

Sound waves can travel in air

1. but not in outer space2. but not in steel.3. but not in water

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Chapters 10,11,12,13,14,15

Consider a guitar string which is one meter long, and produces a note at 440 Hz when plucked from the center.

Where should the string be held to produce a note with frequency of 660 Hz?

The induced current in the loop of wire produces an upward magnetic field inside the loop that opposes the increase in the downward field

associated with the moving magnet.

Variations in air pressure (and density) move through the air in a longitudinal sound wave. The graph

shows pressure plotted against position.

Note: the velocity of sound depends on the medium. It is faster in water than in air, and faster yet in steel.

Speed of Sound 1100 ft/sec (340 m/sec)750 miles per hour

Light travel much, much faster than sound.

Sounds take ~5 second to travel 1 mile

Sounds take ~3 second to travel 1 kilometer

Quiz Question 1:

A piano key produces a note with frequency f = 440 Hz. What is the wavelength of the sound wave this produces in air?

1. 0.77 m

2. 1.3 m

3. 340 m

4. 440 m

5. 149,600 m

The first three harmonics are the

three simplest standing-wave

patterns that can be generated

on a guitar string fixed at both ends.

€

λn =2L

n

n =1,2,3...

€

λn =4L

2n +1

n = 0,1,2,...

Quiz Question 2: (the speed of sound in air is 340 m/sec, the speed of sound in helium is 1300 m/sec)

What is the frequency of the first fundamental of 20 cm tall bottle

A. 340 Hz

B. 1300 Hz

C. 425 Hz

D. 100 Hz

E. 20 Hz

Lecture Question 3:

A speaker is producing a note with frequency 440 Hz. What frequency and wavelength would you hear if you were running towards the speaker?

A. The same frequency and wavelength, 440 Hz.

B. A lower frequency and shorter` wavelength.

C. A higher frequency and higher wavelength.

D. higher frequency and shorter wavelength

E. Lower frequency and higher wavelength

The standing wave patterns for the first three harmonics are shown for a tube open at one end and closed at the other. The curves represent the amplitude of back-and-forth molecular motion at each point in the tube.

Lecture Question 4:

Consider a pipe closed at one end and open at the other, as shown. Choose the correct statement:

A. The pressure is zero at the closed end.

B. Certain harmonics can have nodes at both ends.

C. The harmonic frequencies are integer multiples: f, 2f, 3f,…

D. The fundamental wavelength does not depend on the speed of sound.