Deck 14: Waves

Question 1

Which of these statements can be correctly applied to a wave?

A)Its motion results in the flow of material.
B)Its motion in a medium transfers mass and energy.
C)Its motion in a medium transfers energy.
D)They all require a medium in which to propagate.

Answer 1

Its motion in a medium transfers energy.

Question 2

Figure 14.3 The figure shows two waves.
Two identical waves are in interference. The resultant amplitude will be zero if the phase difference between the waves is __________.

A)2ð
B)ð
C)ð/2
D)ð/4

Answer 2

ð

Question 3

Figure 14.4 Fig. 14.4 shows a standing wave.
A cello C-string vibrates in its fundamental mode with a frequency of 65 Hz. What is the frequency of the harmonic in Fig. 14.4?

A)22 Hz
B)130 Hz
C)195 Hz
D)260 Hz

Answer 3

195 Hz

Question 4

Which of the following equations represents a wave function moving to the right (+x-direction)?

A)y(x, t) = x + 4.0t
B)y(x, t) = (20.0t + x)²
C)y(x, t) = x - 4.0t
D)y(x, t) = (x + 2.0t)²

Question 5

The vibration of a piano's A-string produces a wave with a wavelength of ë = 78 cm, and propagates with a speed of 343 m/s. What is the frequency?

A)0.44 Hz
B)4.40 Hz
C)44.0 Hz
D)440 Hz

Question 6

Which of these waves can experience interference?

A)only sinusoidal waves
B)only longitudinal waves
C)only electromagnetic waves
D)all types of waves

Question 7

A string is under tension. You release the tension to half its previous value. The frequency of the first harmonic

A)decreases by a factor of .
B)increases by factor of 2.
C)does not change, but wavelength reduces to half.
D)decreases by a factor of 4.

Question 8

A wave on a string is represented by the wave function y(x, t) = Asin(kx - ùt). When it reflects at a loose end, what is the wave function of the reflected wave?

A)y(x, t) = Asin(kx - ùt)
B)y(x, t) = -Asin(kx + ùt)
C)y(x, t) = Asin(kx + ùt)
D)y(x, t) = -Asin(kx - ùt)

Question 9

Figure 14.3 The figure shows two waves.
What additional phase difference between the waves in Fig. 14.3 would be needed for the interference of the two waves to be destructive?

A)2ð
B)3ð/2
C)ð
D)ð/2

Question 10

See Fig. 14.4. For a typical high E guitar string with frequency f = 329.6 Hz, what is the ratio between the tensions when it is tuned to the fundamental tone, T_f, and when it is tuned to harmonic, T_h?

A)1/3
B)1/
C)
D)3

Question 11

Which of the following equations represents a wave function moving to the left (-x-direction)?

A)y(x, t) = x - 4.0t
B)y(x, t) = (-20.0t + x)²
C)y(x, t) = x + 4.0t
D)y(x, t) = (x - 2.0t)²

Question 12

Figure 14.1 ​
The figure shows a wave.
The wave from Fig. 14.1 is moving at a speed of 5 cm/s. If L₁ = 6 cm and L₂ = 5 cm, which wave equation describes the wave?

A)y(x, t) = (6 cm)sin[(6.28 s^-1)t - (1.05 cm^-1)x)]
B)y(x, t) = (3 cm)sin[(12.6 s^-1)t - (0.63 cm^-1)x)]
C)y(x, t) = (3 cm)sin[(6.28 s^-1)t - (1.05 cm^-1)x)]
D)y(x, t) = (6 cm)sin[(3.76 s^-1)t - (2.09 cm^-1)x)]

Question 13

Figure 14.2 The figure shows a wave in a rope with two points labelled A and B.
A harmonic wave travelling along the x-axis is described by the equation y(x, t) = (4 cm)sin[(0.5 cm)x - (1.05 s^-1)t)]. What is the wavelength of the wave?

A)0.5 cm
B)1.05 cm
C)4.0 cm
D)12.6 cm

Question 14

Two ropes, A and B, are tied and stretched. Rope A has a linear mass density 9 times higher than rope B. A pulse travels in rope A and continues in B. The speed of the pulse in rope A is v_A, and in rope B it is v_B. What is the relationship between the speeds?

A)v_B = 9v_A
B)v_B = 3v_A
C)v_A = 9v_B
D)v_A = 3v_B

Question 15

Figure 14.3 The figure shows two waves.
What is the phase difference, ÄÖ, between the two waves in Fig. 14.3?

A)2ð
B)3ð/2
C)ð
D)ð/2

Question 16

Figure 14.2 The figure shows a wave in a rope with two points labelled A and B.
A harmonic wave is travelling to the right on a long, stretched rope. Two points on the rope are labelled A and B (see Fig. 14.2). When the wave moves a little to the right, how do these two points move?

A)Both A and B move to the right.
B)Point A moves to the right and B to the left.
C)Point A moves down and B up.
D)Point A moves up and B down.

Question 17

Which wave does NOT belong to the group?

A)infrared
B)ultraviolet
C)ultrasound
D)X-rays

Question 18

String with fixed ends can vibrate in several modes (harmonics). How does the length of a string relate to wavelengths of harmonics?

A)The length of a string contains an integer number of full wavelengths.
B)The length of a string contains an integer number of half wavelengths.
C)The length of a string contains only an odd number of full wavelengths.
D)The length of a string contains only an odd number of half wavelengths.

Question 19

If the speed of a wave increases, how would one of these other parameters change?

A)wavelength increases
B)period increases
C)frequency decreases
D)amplitude increases

Question 20

Figure 14.1 ​
The figure shows a wave.
If L₂ = 65.5 cm, which note from Table 14.1 is represented in Fig. 14.1? Assume that the speed of sound is 343 m/s.

A)G3
B)C4
C)G4
D)C5

Question 21

Two identical waves (having the same wavelength and amplitude) interfere with each other. The initial amplitude of each wave was 28 cm; the resultant wave has an amplitude of 12 cm. What is the phase difference between the waves represented as a fraction of a wavelength?

Question 22

Which note is represented by the wave equation y(x, t) = 2sin[(1642 s^-1)t - (4.79 m^-1)x? For reference, use Table 14.1.

Question 23

A reflected wave on a fixed end is inverted, but does not change shape. A reflected wave on a loose end is not inverted, nor does it change shape.

Question 24

Figure 14.5
​ ​
Fig. 14.5 shows a sound wave.
Fig. 14.5 shows a sound wave in the air. L₁ = 200 ìPa, L₂ = 52.4 cm. Which note from Table 14.1 is represented? What is the amplitude of the wave? Take the speed of sound in the air as 343 m/s.

Question 25

For waves moving at a given speed, the frequency is higher if the wavelength is smaller.

Question 26

The length of a string contains an integer number of halves of wavelengths of harmonics.

Question 27

The frequency of a wave is determined by the source of the wave, but wavelength is not. Wavelength depends on the medium through which the wave propagates.

Question 28

The wave described by the equation y(x, t) = (4 cm)sin[(0.5 cm)x + (1.05 s^-1)t)] is moving along the x-axis in the positive direction (to the right).

Question 29

When a wave passes through a certain medium, the particles of the medium move with the wave. For example, a sound wave propagates through air via air molecules that move from the source to receiver.

Question 30

Bats use ultrasound to locate prey. The wavelength of sound has to be of the order of size of the prey if the prey is to be detected. What is the size of the smallest insect a bat can detect if it emits a sound at 55 kHz? The speed of sound is 343 m/s.

Question 31

Constructive interference occurs only when two harmonious waves arrive at the same point with a phase difference of exactly 1 wavelength.

Question 32

Figure 14.6 Fig. 14.6 shows a sound wave.
What is the amplitude of the wave represented in Fig. 14.6? What are the wavelength and the frequency, assuming that it is a sound wave in air? The speed of sound in air is 343 m/s.

Question 33

Figure 14.5
​ ​
Fig. 14.5 shows a sound wave.
Fig. 14.5 shows a sound wave in the water. L₁ = 220 ìPa, L₂ = 226 cm. Which note from Table 14.1 is represented? What is the amplitude of the wave? Take the speed of sound in the water as 1482 m/s.

Question 34

Describe the difference between reflected waves in these two cases: when the incident wave propagates from a less dense medium to a denser medium, and the opposite case, when the incident wave propagates from a denser medium to a less dense medium.

Question 35

When a wave passes through a certain medium, the particles of the medium move with the wave. For example, a sound wave propagates through air via air molecules, which move from the source to receiver.

Question 36

Whenever a wave reflects off the boundary between denser and less dense medium, in any direction, it will result in an inverted wave.

Question 37

An antenna 72.8 m long has a length equal to ¼ of a wavelength of the produced wave. If the station using this antenna emits a signal of 1030 kHz, what is the speed of the wave?

Question 38

If we add two sine waves at the same point in space, the resultant has to have a larger amplitude than either of individual waves.

Question 39

A cello C-string vibrates in its fundamental mode with a frequency of 60 Hz. In order to tune it to a proper frequency of 65 Hz, how do you adjust the tension?

Question 40

Figure 14.6 Fig. 14.6 shows a sound wave.
What is the amplitude of the wave represented in Fig. 14.6? What are the wavelength and the frequency, assuming that it is a radio wave? The speed of the radio wave is 3 × 10⁸ m/s.