Chapter 6 - Sound and Doppler Effect

Question 1

How do pressure pulses of air travel down a closed pipe?

Answer 1

It travels down to the closed end and is reflected back toward the origin. It reaches the open-end origin, where it is reflected back toward the closed end. It has changed phase (decreased). It is reflected again at the closed end and once it reaches the open-end origin, it changes phase (increases). It continues this cycle.

Question 2

What is the wave interference at an antinode?

Answer 2

constructive

Question 3

Equation: frequency of standing waves in a closed pipe

Answer 3

f_n = nv/4L

n = odd numbers (1, 3, 5, …)

Question 4

Equation: harmonic frequency of a standing wave of a string in terms of fundamental frequency

Answer 4

f_n = nf₁

n = harmonic number

Question 5

Equation: sound intensity level (β)

Answer 5

β = 10 x log (I/I₀)

I₀ = reference sound intensity

Question 6

How far are nodes from each other in a standing wave?

Answer 6

1/2 wavelength

Question 7

What is a standing wave?

Answer 7

a wave that does not appear to move in either direction along the length of a string

Question 8

Equation: speed of sound in ideal gas

Answer 8

v = √γP/ρ = √γRT/M

ρ = gas density

P = gas pressure

γ = Cp/Cv (molar heat capacity at pressure/molar heat capacity at volume)

R = ideal gas constant

T = temperature (K)

M = gas mass

Question 9

Equation: Doppler effect

Answer 9

f_L = [(v +/- v_L)/(v +/- v_s)] x f_s

f_L = frequency encountered by listener

f_s = frequency emitted by source

v_L = speed of the listener relative to the still air (moving toward source = +, moving away from source = -)

v_s = speed of the source relative to the still air (moving toward listener = -, moving away from listener = +)

v = speed of wave in air

Question 10

What is a rarefraction?

Answer 10

an area in a sound wave that has low density

Question 11

How does the fundamental frequency for a closed pipe compare to that of an open pipe?

Answer 11

It is 1/2 the fundamental frequency of an open pipe.

Question 12

If distance increases by a factor of 3.2, how does the intensity of a sound change?

Answer 12

It drops by a factor of 10.

Question 13

What type of wave are sound waves?

Answer 13

longitudinal

Question 14

How do pressure pulses of air travel down an open pipe?

Answer 14

Since it is open on both ends, it travels down to one end, some of it continues out, but the rest is reflected back in. It tracks back toward the origin and some of it continues out, but the rest is reflected back in. It continues this cycle.

Question 15

What is displacement of a string at a node?

Answer 15

0

Question 16

In an open pipe, where are the antinodes of a wave?

Answer 16

at each open end

Question 17

Equation: wavelength of a harmonic wave on a string

Answer 17

λ_n = 2L/n

Question 18

What are harmonics?

Answer 18

frequencies that are integer multiples of the fundamental frequency (f₁)

Question 19

What is displacement of a string at an antinode?

Answer 19

maximum amplitude

Question 20

What is γ for a monatomic gas, diatomic gas, and polyatomic gas?

Answer 20

monatomic = 1.67

diatomic = 1.40

polyatomic = 1.33

Question 21

In a closed pipe, where are the nodes and antinodes of a wave?

Answer 21

The antinode will be at the opening of the pipe, while the node wll be at the closed end of the pipe.

Question 22

What is the order for sound speed in different mediums?

Answer 22

V_solid > v_liquid >v_gas

Question 23

How does speed of sound in a monatomic gas compare to the speed of sound in a polyatomic gas?

Answer 23

speed of sound is faster in a monatomic gas

Question 24

How far are antinodes from each other in a standing wave?

Answer 24

1/2 wavelength

Question 25

What is the intensity of the reference sound for humans?

Answer 25

10^-12 W/m²

Question 26

How far are nodes and antinodes from each other in standing waves?

Answer 26

1/4 wavelength

Question 27

What are overtones?

Answer 27

frequencies greater than the fundamental frequency (f₁)

ex: first overtone = second harmonic

Question 28

How does intensity change with distance?

Answer 28

Intensity decreases with increased distance by a squared factor.

Question 29

Do waves travel faster in warm or cold air?

Answer 29

warm air

Question 30

Equation: wavelength of standing waves in an open pipe

Answer 30

λ_n = 2L/n

Question 31

Equation: beat frequency

Answer 31

fbeat = If₁ - f₂I

Question 32

High frequency sounds are generated by nerves closest/farthest from the oval window?

Answer 32

closest

Question 33

What determines the speed of sound of an object?

Answer 33

The strength of the forces between the molecules in a given medium determines the speed of sound. If the restoring forces are greater, than sound will travel faster.

Question 34

Equation: frequency of harmonic wave on a string

Answer 34

f_n = nv/2L

Question 35

Equation: frequency of standing waves in an open pipe

Answer 35

f_n = nv/2L

Question 36

What is the speed of sound in air at room temerature?

Answer 36

~340m/s

Question 37

For every drop in intensity by a factor of 10, how does this affect the decibel level?

Answer 37

Decibel level decreases by 10.

Question 38

What are the units of sound intensity?

Answer 38

J/(m²s) = W/m²

Question 39

What is the wave interference at a node?

Answer 39

destructive

Question 40

What is the Doppler effect?

Answer 40

the change in pitch of a sound (or any wave) from a high frequency as it approaches an observer to a low frequency as it moves away from the observer

Question 41

What affects sound loudness/intensity?

Answer 41

amplitude (higher amplitude = louder)

Question 42

What are the units of intensity level?

Answer 42

decibel (dB)

Question 43

How do you solve for an echo problem?

Answer 43

plug into the Doppler equation twice (you may need to change signs based on who is the source/listener)

Question 44

Equation: wavelength of standing waves in a closed pipe

Answer 44

λ_n = 4L/n

n = odd numbers (1, 3, 5, …)

Question 45

Equation: intensity of sound in terms of power and energy

Answer 45

I = Power/Area = Energy/(Area x Time)

Question 46

What affects sound pitch?

Answer 46

frequency (higher frequency = higher pitch)

Question 47

Consecutive harmonics differ by how much in frequency?

Answer 47

the fundamental frequency