Chapter 17: Waves II Flashcards
A sound wave is… This means that there are alternating ___ and ___ pressure regions that propagate through the medium.
A longitudinal wave traveling through a medium that involves alternating compression and rarefaction of the medium.
High; low.
What is rarefaction?
Expansion.
What is pressure (P)?
The force per unit area exerted by a fluid (liquid or gas) on walls of its container (due to molecular collisions).
What is the SI unit for pressure?
N/(m^2), or Pa (pascal).
What is the pressure of a column of air at STP?
1.01 x 10^5 Pa
What is STP?
Standard temperature and pressure; the pressure at sea level and a temperature of exactly 0 degrees Celsius.
The speed of sound in a medium is…
The square root of the medium’s elastic property divided by the medium’s inertial property.
What is the elastic property (B)?
The bulk modulus of the medium, or the pressure increase over the fractional change in volume of the medium.
SI unit: m/s
The elastic property is a measure of the ___ of the medium; the higher the B value, the (easier)/(harder) it is to ___.
Stiffness; harder; compress.
Both B and ρ depend on temperature, so therefore v (does)/(does not) depend on temperature.
Does.
The frequency of a sound wave trapped in an airtight tube capped with a piston is dictated by…
The motion of that aforementioned piston.
The movement of a piston capping an airtight tube causes “waves” of ___ in the air, with areas of ___ between them.
Compressions; low pressure.
The particles moving as a result of the wave ___, and (do)/(do not) continuously travel forwards with the “waves”.
Oscillate; do not.
What is the displacement of a fluid element from equilibrium?
s(x,t) = s(subs)cos(kx - ωt)
Δp(x,t) = …
Δp(subm)sin(kx - ωt)
How far out of phase is the change in pressure from the displacement of particles in sound waves?
1/4 cycle out of phase.
What is the relationship between the displacement amplitude and the pressure amplitude?
Δp(subm) = vρωs(subs)
Describe fully constructive interference of two sound waves.
ϕ = (2m)π
ΔL/λ = m
Describe fully destructive interference of two sound waves.
ϕ = (2m + 1)π
ΔL/λ = m + 0.5
To get the next highest/lowest frequency for constructive or destructive interference, simply add ___ to m.
1.
What is the Doppler Effect?
The change in observed frequency of a wave when the soruce or detector moves relative to the medium.
When the detector moves closer to the source of the sound wave, it intercepts sound waves (more quickly)/(slower), hence a ___ frequency.
More quickly; higher.
If the source is moving towards the detector, use a ___ in the denominator of the frequency equation for a moving source.
Negative sign.
If the source is moving away from the detector, use a ___ in the denominator of the frequency equation for a moving source.
Positive sign.
If the detector is moving towards the source, use a ___ in the denominator of the frequency equation for a moving source.
Positive sign.
If the detector is away from the source, use a ___ in the denominator of the frequency equation for a moving source.
Negative sign.
