Chapter 17: Waves II

Question 1

A sound wave is… This means that there are alternating ___ and ___ pressure regions that propagate through the medium.

Answer 1

A longitudinal wave traveling through a medium that involves alternating compression and rarefaction of the medium.
High; low.

Question 2

What is rarefaction?

Answer 2

Expansion.

Question 3

What is pressure (P)?

Answer 3

The force per unit area exerted by a fluid (liquid or gas) on walls of its container (due to molecular collisions).

Question 4

What is the SI unit for pressure?

Answer 4

N/(m^2), or Pa (pascal).

Question 5

What is the pressure of a column of air at STP?

Answer 5

1.01 x 10^5 Pa

Question 6

What is STP?

Answer 6

Standard temperature and pressure; the pressure at sea level and a temperature of exactly 0 degrees Celsius.

Question 7

The speed of sound in a medium is…

Answer 7

The square root of the medium’s elastic property divided by the medium’s inertial property.

Question 8

What is the elastic property (B)?

Answer 8

The bulk modulus of the medium, or the pressure increase over the fractional change in volume of the medium.
SI unit: m/s

Question 9

The elastic property is a measure of the ___ of the medium; the higher the B value, the (easier)/(harder) it is to ___.

Answer 9

Stiffness; harder; compress.

Question 10

Both B and ρ depend on temperature, so therefore v (does)/(does not) depend on temperature.

Answer 10

Does.

Question 11

The frequency of a sound wave trapped in an airtight tube capped with a piston is dictated by…

Answer 11

The motion of that aforementioned piston.

Question 12

The movement of a piston capping an airtight tube causes “waves” of ___ in the air, with areas of ___ between them.

Answer 12

Compressions; low pressure.

Question 13

The particles moving as a result of the wave ___, and (do)/(do not) continuously travel forwards with the “waves”.

Answer 13

Oscillate; do not.

Question 14

What is the displacement of a fluid element from equilibrium?

Answer 14

s(x,t) = s(subs)cos(kx - ωt)

Question 15

Δp(x,t) = …

Answer 15

Δp(subm)sin(kx - ωt)

Question 16

How far out of phase is the change in pressure from the displacement of particles in sound waves?

Answer 16

1/4 cycle out of phase.

Question 17

What is the relationship between the displacement amplitude and the pressure amplitude?

Answer 17

Δp(subm) = vρωs(subs)

Question 18

Describe fully constructive interference of two sound waves.

Answer 18

ϕ = (2m)π
ΔL/λ = m

Question 19

Describe fully destructive interference of two sound waves.

Answer 19

ϕ = (2m + 1)π
ΔL/λ = m + 0.5

Question 20

To get the next highest/lowest frequency for constructive or destructive interference, simply add ___ to m.

Answer 20

1.

Question 21

What is the Doppler Effect?

Answer 21

The change in observed frequency of a wave when the soruce or detector moves relative to the medium.

Question 22

When the detector moves closer to the source of the sound wave, it intercepts sound waves (more quickly)/(slower), hence a ___ frequency.

Answer 22

More quickly; higher.

Question 23

If the source is moving towards the detector, use a ___ in the denominator of the frequency equation for a moving source.

Answer 23

Negative sign.

Question 24

If the source is moving away from the detector, use a ___ in the denominator of the frequency equation for a moving source.

Answer 24

Positive sign.

Question 25

If the detector is moving towards the source, use a ___ in the denominator of the frequency equation for a moving source.

Answer 25

Positive sign.

Question 26

If the detector is away from the source, use a ___ in the denominator of the frequency equation for a moving source.

Answer 26

Negative sign.