Waves and sound Flashcards
Transverse waves
have oscillations of wave particles, perpendicular to the direction of wave propagation
Longitudinal waves
have oscillations of wave particles parallel to the direction of wave propagation
Displacement (x)
in a wave refers to how far a point is from the equilibrium position, expressed as a vector quantity.
amplitude (A)
of wave is the magnitude of its maximal displacement
crest
max point of a wave ( point of most positive displacement)
trough
minimum point of a wave (point of most negative displacement)
Wavelength (λ)
the distance between two crests or troughs
frequency (f)
the number of cycles it makes per second. It is expressed in hertz (Hz)
Angular frequency (w)
another way of expressing frequency and is expressed in radians per second
w = 2πf = 2π/T
Period (T)
the number of seconds it takes to complete a cycle. It is inverse of frequency . T = 1/f
Interference
the ways in which waves interact in space to form resultant wave.
Constructive interference
occur when waves are exactly in phase with each other. The amplitude of the resultant wave is equal to the sum of the amplitudes of the two interfering waves .
Destructive interference
occurs when waves are exactly out of phase with each other. The amplitude of the resultant wave is equal to the difference in amplitude between the two interfering waves.
Partially constructive and partially destructive interference
occur when two waves are not quite perfectly in or out of phase with each other. the displacement of the resultant wave is equal to the sum of the displacements of the two interfering waves.
Traveling waves
have continuously shifting points of maximum and minimum displacement
Standing waves
produced by the constructive and destructive interference of two waves of the sam frequency traveling in opposite direction in the same space.
antinodes
points of maximum oscillation
Resonance
the increase in amplitude that occurs when a periodic force is applied at the natural (resonant ) frequency.
Damping
decrease in amplitude caused by an applied or nonconservative force
Sound
produced by a mechanical disturbance of a material that creates an oscillation of molecules in the material . Propagates through all forms of matter (but no a vacuum). With a medium, density increases, the speed of sound decreases
The pitch
sound is related to its frequency
Doppler effect
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. When source and detector are moving toward each other the apparent frequency will be higher than the emitted. When they are moving away the apparent will be lower. If the two objects are moving in the same direction, they can be high, lower, or equal depending on speed. When the source is move at or above the speed of sound, sonic booms or shock waves can form.
f’ =f (v+- vD)/(v-+vs)
sound level
loudness or volume of sound. Related to intensity. Intensity is related to a wave’s amplitude. Intensity decreases over distance and some energy is lost to attenuation (damping) from frictional forces.
B = 10 log I/Io
What can support standing waves?
open pipes and strings, the length of the string or pupe is equal to some or multiple of half wave-lengths.
wave speed
v=fλ
intensity
I = P/A
change in sound level
Bf = Bi + 10 og If/Ii .
wavelength of standing waves (strings and open pipes)
λ = 2L/n
Frequency of a standing wave (strings and open pipes)
f =nv/2L
Wavelength of a standing wave (closed pipes)
λ = 4L/n
Frequency of a standing wave (closed pipes)
f = nv/4L
