Waves and Sound Flashcards
have oscillations of wave particles perpendicular to the direction of wave propagation (movement) (e.g. electromagnetic waves)
transverse waves
have oscillations of wave particles parallel to the direction of wave propagation (e.g. sound waves)
longitudinal waves
refers to how far a point is from the equilibrium position in a wave, expressed as a vector quantity
displacement (x)
magnitude of maximal displacement of wave
amplitude (A)
maximum point of wave, point of most positive displacement
crest
minimum point of wave, point of most negative displacement
trough
distance between two crests or troughs of wave
wavelength (λ)
number of cycles a wave makes per second; expressed in Hertz (Hz)
frequency (ƒ)
frequency (ƒ)
v = ƒλ
where:
v = propagation speed
λ = wavelength
number of seconds a wave takes to complete a cycle; inverse of frequency
period (T)
period (T)
T = 1/ƒ
where:
ƒ = frequency
another way of expressing frequency; expressed in radians/second (rad/sec)
angular frequency (ω)
angular frequency (ω)
ω = 2πƒ = 2π/T
where:
ƒ = frequency
T = period
describes the ways in which waves interact in space to form a resultant wave
interference
type of interference:
occurs when waves are exactly in phase with each other; amplitude of resultant wave equals sum of two interfering waves
constructive interference
type of interference:
occurs when waves are exactly out of phase with each other; amplitude of resultant wave equals difference of two interfering waves
destructive interference
type of interference:
occurs when two waves are not quite perfectly in or out of phase with each other; the displacement of the resultant wave equals the sum of the displacement of the two interfering waves
partially constructive or destructive interference
have continually shifting points of maximum and minimum displacement
traveling waves
are produced by the constructive and destructive interference of two waves of the same frequency traveling in opposite directions in the same space
standing waves
points of maximum oscillation
antinodes
points where there is no oscillation
nodes
the increase in amplitude that occurs when a periodic force is applied at the natural (resonant) frequency of an object
resonance
a decrease in amplitude caused by an applied or nonconservative force
damping (attenuation)
is produced by mechanical disturbance of a material that creates an oscillation of the molecules in the material; propagates through all forms of matter (but not a vacuum); propagates fastest through solids, then liquids, and slowest through gases; as density of medium increases the speed of sound decreases
sound
speed of sound through a medium (v)
v = √(B/ρ)
where:
B = Bulk modulus
ρ = density
a measure of the medium’s resistance to compression; increases from gas to liquid to solid
Bulk modulus (B)
our perception of the frequency of sound
pitch
a shift in the perceived frequency of a sound compared to the actual frequency of the emitted sound when the source of the sound and its detector are moving relative to one another
Doppler effect
Doppler effect
ƒ’ = ƒ ((v ± v(D)) / (v ∓ v(S))
where: ƒ' = perceived frequency ƒ = actual frequency v = speed of sound in medium v(D) = speed of detector v(S) = speed of source
signs:
top sign- used when source and detector moving toward one another
bottom sign- used when source and detector moving away from one another
will be higher than emitted frequency when the source and detector are moving toward each other; will be lower than emitted frequency when the source and detector are moving away from each other
apparent frequency
can occur when source is moving at or above the speed of sound
shock wave (sonic boom)
the way in which we perceive the intensity of a sound
loudness or volume of sound
average rate of energy transfer per area across a surface that is perpendicular to the wave; power transported per unit area; units = W/m^2 (W is watts); decreases over distance and some energy is lost to damping (attenuation) from frictional forces
intensity
intensity (I)
I = P/A
where:
P = power
A = area
support standing waves, and the length is equal to some multiple of half-wavelengths
strings and open pipes
a positive, nonzero integer that corresponds to the number of half-wavelengths supported
harmonic of string or open pipe (n)
equation that relates wavelength of standing wave and length of string or open pipe:
λ = 2L/n
where:
λ = wavelength
L = length
n = harmonic (1,2,3,…)
equation of possible frequencies of string or open pipe:
ƒ = nv/2L
where: ƒ = frequency n = harmonic (1,2,3,...) v = wave speed L = length
number of antinodes will tell you which harmonic it is
string
number of nodes will tell you which harmonic it is
open pipe
the lowest frequency (longest wavelength) of a standing wave that can be supported in a given length of string or pipe; given by n=1
fundamental frequency (first harmonic)
second harmonic = ____
third harmonic = ____
…
first overtone
second overtone
all the possible frequencies that a string or pipe can support
harmonic series
support standing waves, length is equal to some odd multiple of quarter-wavelengths
closed pipe
a positive, nonzero, odd integer that corresponds to the number of quarter-wavelengths supported
harmonic of closed pipe (n)
equation that relates wavelength of standing wave and length of closed pipe:
λ = 4L/n
where:
λ = wavelength
L = length
n = harmonic (1,3,5,…)
equation of possible frequencies of closed pipe:
ƒ = nv/4L
where: ƒ = frequency n = harmonic (1,3,5,...) v = wave speed L = length
medical application of sound, used for both imaging (diagnostic) and treatment (therapeutic) purposes
ultrasound
