Waves & Sound Flashcards
What are sinusoidal waves?
Individual particles oscillate back and forth with a displacement that follows a sinusoidal pattern
May be transverse or longitudinal
What are transverse waves?
The direction of oscillation is perpendicular to the direction of propagation of the wave
“The Wave” at a stadium
Electromagnetic waves - visible light, microwaves, Xrays
What are longitudinal waves?
The particles of the wave oscillate parallel to the direction of propagation of the energy transfer
Sound waves
Oscillate through cycles of compression and rarfaction (decompression) along the direction of motion
Wavelength? (λ)
One entire wave cycle
Distance from one max of the wave to the next
Frequency? (f)
Number of wavelengths passing a fixed point per second
Measured in Hertz (Hz) or cycles per second (cps)
Equation for speed of a wave (v)?
V=fλ
Velocity=frequency x wavelength
Period (T) and equation?
The number of seconds per cycle
T=1/f
Angular frequency (ω) and equation?
Scalar measure of rotation rate; the rate of change of the phase of a sinusoidal waveform
ω= 2πf = 2π/T
At what “position” or symmetry do waves oscillate about?
Equilibrium position
Amplitude?
Maximum magnitude of displacement of a wave from the equilibrium position (1/2 the total height)
What does it mean if two waves are “in phase” and what is their phase difference?
Two waves have same frequency, wavelength, and amplitude pass through the same space at the same time because their crests and troughs coincide
phase difference = 0
What does it mean if two waves are “out of phase” and what is their phase difference?
Two waves traveling do not align perfect by crests and troughs
*If the crest of one aligned with the trough of another
phase difference = 1/2 of a wave OR λ/2 OR 180°
What is the principle of superposition?
when waves interact with each other, the displacement of the resultant wave at any point is the sum of the displacements of the two interacting waves
What is constructive interference?
When waves are perfectly in phase, the displacements always add together and the amplitude is equal to the sum of the amplitudes of the two waves
What is destructive interference?
When waves are perfectly out of phase, the displacements always counteract each other and the amplitude is the difference between the two waves
What type of interference occurs is two waves interact that are not perfectly in phase or out of phase?
partially constructive and partially destructive
What happens to the pattern of a traveling wave once it hits a fixed boundary? Nonfixed boundary?
Fixed boundary: The wave will be reflected and inverted back to the source
Nonfixed boundary: The wave will be reflected back to the source in the same orientation
What happens when there is interference between the reflected wave and the original wave - what kind of wave forms and explain it?
Forms a standing wave
Only apparent movement of the wave is fluctuation of amplitude at fixed points along the length of the string between nodes
What is timbre?
the quality of sound determined by the natural frequency
What happens when there is a forced oscillation? What are the two possible outcomes based on frequency?
system will be driven at a frequency equal to the frequency of the force
If the forced frequency equals the natural frequency, the amplitude will increase
If the forced frequency does NOT equal the natural frequency then the object will not have a distinguished pattern of oscillation
What is resonance?
When the frequency of the applied force is equal to the natural (resonant) frequency of the system causing the amplitude to reach a maxium
What is damping?
Decrease in amplitude of a wave due to an applied force or nonconservative force
What type of wave is a sound wave?
Longitudinal
Can sound travel through a vacuum?
No
What is the equation for speed of sound?
v= SQRT(B/ρ)
where B=bulk modulus - medium’s resistance to compression (increases from gas to liquid to solid)
In which medium does sound travel the fastest? Slowest?
Fastest: Solid
Middle: Liquid
Slowest: Gas
What is the speed of sound in air at 20°C?
343 m/s
What is the speed of sound in air at 20°C?
343 m/s
How is sound produced/carried?
Sound is produced by disturbances of particles which causes oscillation of molecules about their equilibrium position causing compression and rarefaction along the direction of propagation forming a longitudinal wave
What is pitch and how is related to frequency?
Pitch is the perception of frequency
low frequency = low pitch and vice versa
What is the normal range of frequency heard by humans?
Between 20 - 20,000 Hz
What are sound waves below 20 Hz? Above 20,000 Hz?
Below 20: infrasonic
Above 20,000: ultarsonic
What is the Doppler effect?
Describes the difference between actual frequency and perceived frequency of sound when the source and detector are moving relative to each other
How does frequency change if the source and detector are moving towards each other (in respect to Doppler effect)?
The perceived frequency will be greater than the actual frequency
How does frequency change if the source and detector are moving away from each other (in respect to Doppler effect)?
The perceived frequency will be less than the actual frequency
What is the equation to explain the Doppler effect?
f ‘ = f (v±Vd)/(v±Vs)
What is the equation to explain the Doppler effect?
f ‘ = f (v±Vd)/(v±Vs)
f ' = perceived frequency f = actual frequency v = speed of sound in medium Vd = speed of detector Vs = speed of source
What is the equation to explain the Doppler effect?
f ‘ = f (v±Vd)/(v∓Vs)
f ' = perceived frequency f = actual frequency v = speed of sound in medium Vd = speed of detector Vs = speed of source
*Top for towards
bottom for away
What is a shock wave?
Highly condesnsed wave front due to an object traveling at or faster than the speed of light
What is the degree of compression of medium relate to in sound?
Amplitude
What can one hear a sonic boom?
Any time that an object passes a detector
