Question 1

Sound A has a high pitch and sound B has a low pitch. Which of the following statements about these two sounds are correct? (There could be more than one correct choice.)

Accepted Answer

B) High-pitched sounds have shorter periods because their waves cycle faster. C) High-pitched sounds have greater frequencies, as pitch directly correlates with frequency.

Question 2

What is the frequency of the wave shown in the figure?

Accepted Answer

A

Question 3

What characteristics of a sound wave are related to the "pitch" of a musical note? (There could be more than one correct choice.)

Accepted Answer

B, C, D

Question 4

When a certain string is under tension T, the speed of a wave in the string is v. What will be the speed of a wave in the string if the tension is increased to 2T without changing the mass or length of the string?

Accepted Answer

The speed of a wave on a string is given by the formula $ v = \sqrt{\frac{T}{\mu}} $, where $ T $ is the tension and $ \mu $ is the linear mass density. If the tension is increased to 2T, the new speed $ v' $ is $ v' = \sqrt{\frac{2T}{\mu}} = \sqrt{2} \cdot \sqrt{\frac{T}{\mu}} = v \sqrt{2} $.

Question 5

In many cartoon shows, a character runs off a cliff, realizes his predicament, and lets out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage point of an observer at the top of the cliff leaning over the edge, the pitch of the scream as he falls should be

Accepted Answer

As the character falls, they will be moving away from the observer at the top of the cliff. This will cause a Doppler shift in the sound waves of their scream, resulting in a lower pitch. Additionally, the character's speed will increase as they fall, causing the sound waves to have a longer wavelength and lower frequency, further contributing to the lowering of the pitch. Therefore, the scream should be lower than the original pitch and decreasing as he falls.

Question 6

The intensity of the waves from a point source at a distance d from the source is I. At what distance from the sources is the intensity equal to 2I?

Accepted Answer

The intensity of a wave from a point source is inversely proportional to the square of the distance from the source (I ∝ 1/d²). To double the intensity (2I), the distance must be reduced by a factor of √2, hence the distance is d/√2.

Question 7

Why does the intensity of waves from a small source decrease with the square of the distance from the source?

Accepted Answer

The intensity of waves from a small source decreases with the square of the distance from the source because the waves spread out as they travel. This means that the energy from the waves is being distributed over a larger and larger area as they move away from the source. As the area over which the energy is spread out increases, the intensity of the waves decreases, following an inverse square law relationship.

Question 8

Seven seconds after a brilliant flash of lightning, thunder shakes the house. Approximately how far was the lightning strike from the house?

Accepted Answer

The answer of Seven seconds after a brilliant flash of...

Question 9

A string of mass m is under tension, and the speed of a wave in the string is v. What will be the speed of a wave in the string if the mass of the string is increased to 2m but with no change in the length or tension?

Accepted Answer

The answer of A string of mass m is under...

Question 10

As you are moving very quickly toward a speaker emitting a pure tone, which characteristics of the sound get larger? (There may be more than one correct choice.)

Accepted Answer

As you move quickly towards a source of sound, the frequency of the sound wave will increase. This is known as the Doppler effect. As the frequency increases, the perceived pitch of the sound will also increase. Additionally, the loudness of the sound will also increase as you move closer to the source, due to the increase in amplitude of the sound wave.

Question 11

A string of length L is under tension, and the speed of a wave in the string is v. What will be the speed of a wave in the string if the length is increased to 2L but with no change in the mass or tension?

Accepted Answer

The speed of a wave in a string is given by v = $\sqrt { T/\mu }$, where T is the tension and \mu is the linear mass density. If the length of the string is increased to 2L, the linear mass density will be reduced to \mu/2. Therefore, the speed of the wave will become v' = $\sqrt { T/(\mu/2) } = \sqrt { 2T/\mu } = v \sqrt { 2 }$.

Question 12

You double your distance from a sound source that is radiating equally in all directions. What happens to the intensity of the sound? It reduces to

Accepted Answer

The intensity of sound decreases with the square of the distance from the source. Therefore, if the distance is doubled, the intensity becomes (1/2)^2 = 1/4 of its original value.

Question 13

Four waves are described by the following equations, where distances are measured in meters and times in seconds. I. y = 0.12 cos(3x - 21t)
II. y = 0.15 sin(6x + 42t)
III. y = 0.13 cos(6x + 21t)
IV. y = -0.23 sin(3x - 42t)
-
Which of these waves have the same speed?

Accepted Answer

The answer of Four waves are described by the following...

Question 14

Suppose that a sound source is emitting waves uniformly in all directions. If you move to a point twice as far away from the source, the frequency of the sound will be

Accepted Answer

The frequency of the sound wave is not affected by the distance from the source. It remains unchanged.

Question 15

Four waves are described by the following equations, where distances are measured in meters and times in seconds. I. y = 0.12 cos(3x - 21t)
II. y = 0.15 sin(6x + 42t)
III. y = 0.13 cos(6x + 21t)
IV. y = -0.23 sin(3x - 42t)
-
Which of these waves have the same period?

Accepted Answer

The period of a wave is determined by the coefficient of $t$ in the argument of the sine or cosine function, which is related to the angular frequency $\omega$. Waves I and III have the same absolute value for the coefficient of $t$ (21), indicating they have the same period. Similarly, waves II and IV have the same absolute value for the coefficient of $t$ (42), indicating they also share the same period.

Question 16

A fisherman fishing from a pier observes that the float on his line bobs up and down, taking 2.4 s to move from its highest point to its lowest point. He also estimates that the distance between adjacent wave crests is 48 m. What is the speed of the waves going past the pier?

Accepted Answer

The time it takes for one wave crest to pass by the pier is equal to the time it takes for the float to move from its highest point to its lowest point. This time is equal to the period, T. Therefore:

T = 2.4 s

The distance between adjacent wave crests is equal to the wavelength, λ. Therefore:

λ = 48 m

The speed of the wave can be calculated using the formula:

v = λ / T

Substituting the values of λ and T, we get:

v = 48 m / 2.4 s = 20 m/s

Therefore, the answer is (C) 10 m/s.

Question 17

The intensity of the waves from a point source at a distance d from the source is I. What is the intensity at a distance 2d from the source?

Accepted Answer

The intensity of waves from a point source follows the inverse square law, meaning it is inversely proportional to the square of the distance from the source. Therefore, if the distance is doubled (from d to 2d), the intensity becomes one-fourth (I/4) of the original intensity.

Question 18

What is the wavelength of the wave shown in the figure?

Accepted Answer

The answer of What is the wavelength of the wave...

Question 19

In many cartoon shows, a character runs off a cliff, realizes his predicament, and lets out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage point of an observer at the foot of the cliff, the pitch of the scream as he falls should be

Accepted Answer

As the character falls, their velocity increases, which causes the frequency and pitch of the scream to increase. This is known as the Doppler effect. Therefore, the pitch of the scream would be higher than the original pitch and increasing as the character falls.

Question 20

Which one of the curves shown in the figure best represents the variation of wave speed v as a function of tension for transverse waves on a stretched string?

Accepted Answer

The answer of Which one of the curves shown in...

Quiz 15: Traveling Waves and Sound