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Exam 14: Waves

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Question 1

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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

E) A) and B)
F) A) and C)

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Question 2

Multiple Choice

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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.

E) All of the above
F) A) and C)

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Question 3

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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 __________.

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.

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.

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.

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.

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.

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?

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?

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?

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

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?

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.

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.

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.

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.

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

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

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