Physics Chapter 8: Waves and Sound Flashcards
Equation for the velocity of sound
B = bulk modulus
Bulk modulus
measures how much pressure is needed to compress a substance by a certain amount
Sound moves fastest in solids because solids are
Non-compressible
Intensity is defined by
Power divided by area
Standing waves occur when
Waves are reflected back in a constrained medium
Equations for wavelength and frequency for open pipes and strings
But strings have NODES at both ends (fixed ends)
Open pipes have ANTINODES at both ends
Equation for wavelength and frequency for closed pipes
M is supposed to be wavelength (error)
And ONLY USE ODD INTEGERS
For fixed strings, harmonic is equal to
Number of antinodes
For open pipes, the harmonic is equal to
Number of nodes
To verify a period on a graph, look for the waveform’s
Zero-crossing (points where it crosses the x-axis). Look for where the the waveform begins to REPEAT. For example the top image has the first 3 harmonics. The first harmonic contributes to the period whereas the other harmonics contribute to the shape
Doppler effect equation (Approximation for relatively slow speeds such as sound)
I still don’t fully understand this but maybe this will be helpful
Formula for observed frequency (Doppler effect)
Blue shift characteristics
Motion: source moving TOWARDS observer
Wavelength: shortens
Frequency: increases
Color: moves to blue
Energy: higher energy photons
Red shift characteristics
Motion: Source moving away from observer
Wavelength: increases
Frequency: decreases
Color: shifts toward red
Energy: lower energy photons
Loudness is a change in
amplitude
Timbre
Most sounds are not pure tones but a combination of a fundamental frequency (the lowest frequency) and its harmonics or overtones (multiples of the fundamental). Timbre arises from the specific pattern and intensity of these harmonics.
Pitch is a change in
frequency. Increase in pitch = higher frequency, decrease in pitch = lower frequency
What is the frequency of the lowest pitched tone produced by the bottle whistle in Figure 2?
First find the period of the lowest pitch (ie lowest frequency) = ~0.002.
f = 1/T
1/0.002 = 500Hz
Wavelength for closed pipe
λ = 4L/n
n: Harmonic number (only odd harmonics are allowed: n=1,3,5,…)
Wavelength for open pipe
λ = 2L/n
n= harmonics
Antinode vs node
Antinode = maximum amplitude
node = minimum amplitude
How many nodes/antinodes for first 3 harmonics in a closed tube
REMEMBER CLOSED PIPES YOU CAN ONLY USE ODD INTEGERS
therefore fundamental harmonic = 1 nodes, 1 antinodes
3rd harmonic = 2 nodes, 2 antinodes
5th harmonic = 3 nodes, 3 antinodes
How many nodes/antinodes for first 3 harmonics in an open tube
fundmental = 2 antinodes, 1 node
2nd harmonic = 3 antinodes, 2 nodes
3rd harmonic = 4 antinodes, 3 nodes
Sounds move faster or slower in warmer air?
Sounds moves FASTER
Warmer air has more kinetic energy
this increases number of collisions between molecules, speeding up sound transmission
Loudness vs intensity
Intensity is a PHYSICAL property. objective measure of sound energy per unit area. ( I = Power of sound wave/m2)
Loudness is a perceived property. subjective perception of sound intensity by the human ear. Measured in decibels
In other words, decibels are actually a way of expressing intensity relative to a reference intensity.
EMR is what kind of wave
Transverse
Sound is what kind of wave
longitudinal
If two materials have the same elasticity (same value for B in terms of the bulk modulus), does speed of sound travel faster in more or less dense material?
Faster in less dense material because denser materials have more mass per unit volume, meaning each particle has more inertia.
Time period of a simple pendulum
