Waves and Sound

Question 1

What is the difference between Transverse and Longitudinal waves?

Answer 1

Transverse: perpendicular to the propagation of the wave’s direction. ex. electromagnetic wave
Longitudinal: Parallel to the wave’s direction. ex. sound wave

Question 2

How is the velocity of a wave is related to frequency and wavelength?

Answer 2

v = fλ (Hz or s^-1)(usually in nm)

Question 3

What is the relationship between Frequency and Period?

Answer 3

f = 1/T

Question 4

What is the equation for angular frequency? What does it measure?

Answer 4

ω = 2pi(f)

Angular displacement per unit of time

Question 5

What is the difference between Traveling and Standing waves?

Answer 5

Traveling: wave is moving
Standing: wave is not moving because of the reflecting wave constructively interferes with the incident wave and destructively interferes w/ at a “node”

Question 6

What are nodes and antinodes?

Answer 6

node: point where the wave does not move
antinode: half way between two nodes

Question 7

What is the audible frequency for human?

Answer 7

20Hz ~ 20,000Hz

Question 8

How does the medium’s density determine the speed of sound(v)?

Answer 8

more dense -> faster it travels.

Solid(fastest)….Air(slowest)

Question 9

What is Doppler effect and what is the equation?

Answer 9

Doppler effect is a phenomenon where one hears higher pitch(perceived frequency) of a sound when the source is traveling closer to the observer.
f’ = f(v + v(d))/(v - v(s)) if detector/source is moving toward the other
f’ = f(v - v(d))/(v+ v(s)) if detector/source is moving away from the other

Question 10

What is the equation for Intensity and Loudness of sound?

Answer 10

I = P/A
I: Intensity(W/m^2)
P: Power
A: Cross area

Question 11

How to calculate Decibel(dB)?

Answer 11

β = 10 log(I/I(ref))

I(ref): threshold of hearing used as a reference = 1 x 10^-12 W/m^2

Question 12

How to calculate Decibel with new intensity?

Answer 12

βf = βi + 10 log [I(f)/I(i)]

Question 13

What is a harmonic?

Answer 13

natural frequency that occurs within an object that produces standing wave patterns

Question 14

Explain how to get the number of harmonics in three cases: 1) String, 2) Open pipes, and 3) Closed pipe. Draw them out

Answer 14

String: # of Antinodes
Open pipes: # of nodes
Closed pipes: # of 1/4-wavelengths

Question 15

Closed pipes can only produce odd-number of harmonics (T/F)

Answer 15

True

Question 16

What is the equation used to calculate the wavelength and the frequency of the standing waves in strings, open pipes, and closed pipes?

Answer 16

String and open pipes: λ = 2L/n and f = nv/2L

Closed pipes: λ = 4L/n and f nv/4L

Question 17

What is the relationship between number of harmonics and their frequencies?

Answer 17

harmonic frequencies are related to each other by whole number ratio.
If 1st harmonic frequency is 1000Hz, then 3rd harmonic frequency will be 3000Hz.

Question 18

What is the relationship between harmonic frequency and the wave speed(v)?

Answer 18

As frequency gets higher, the wavelength gets shorter, and according to the eq: v = fλ, the speed will remain the same in various harmonics too.