Q: A sound wave in air at 20°C has a frequency of 500 Hz. What is its wavelength? (Speed of sound in air at 20°C is 343 m/s)

$$\lambda = \frac{343}{500} = 0.686\ \text{m}$$

Q: A bat uses echolocation to detect a wall 40 m away. If the speed of sound is 340 m/s, how long after emitting a pulse does the bat hear the echo?

$$t = \frac{2 \times 40}{340} = 0.235\ \text{s}$$

Q: A 100 Hz sound wave travels at 343 m/s. What is the phase difference between two points 0.60 m apart?

$$\Delta \phi = 2\pi \frac{0.60}{3.43} = 1.10\ \text{rad}$$

Q: A solar cell array with an area of $$2.0\ \text{m}^2$$ and efficiency of 12% is exposed to sunlight with intensity $$1300\ \text{W/m}^2. $$What is the maximum power output?

$$P = 0.12 \times 1300 \times 2.0 = 312\ \text{W}$$

Q: The sound intensity level at a rock concert is 120 dB. What is the intensity in $$\text{W/m}^2$$?

$$I = 1.0 \times 10$$^{0}$$\ \text{W/m}^2$$

Question 1

Which of the following best describes the difference between a transverse wave and a longitudinal wave?

Accepted Answer

In a transverse wave, particles of the medium move perpendicular to the direction of wave propagation, while in a longitudinal wave, particles move parallel to the direction of wave propagation.

Question 2

A wave on a string is described by $$D(x, t) = A \sin(kx - \omega t + \$$phi_0$$). $$What is the speed of this wave?

Accepted Answer

$$v = \frac{\omega}{k}$$

Question 3

Which of the following statements about mechanical waves is correct?

Accepted Answer

Mechanical waves require a medium to propagate.

Question 4

A sound wave in air at 20°C has a frequency of 500 Hz. What is its wavelength? (Speed of sound in air at 20°C is 343 m/s)

Accepted Answer

$$\lambda = \frac{343}{500} = 0.686\ 	ext{m}$$

Question 5

The speed of a wave on a stretched string is given by $$v = \sqrt{\frac{T_s}{\mu}}. If $$the tension $$T_s is $$quadrupled, what happens to the wave speed?

Accepted Answer

It doubles.

Question 6

A bat uses echolocation to detect a wall 40 m away. If the speed of sound is 340 m/s, how long after emitting a pulse does the bat hear the echo?

Accepted Answer

$$t = \frac{2 	imes 40}{340} = 0.235\ 	ext{s}$$

Question 7

Which of the following is true about the speed of sound in different media?

Accepted Answer

The speed of sound is highest in solids and lowest in gases.

Question 8

A sinusoidal wave has an amplitude $$A$$, frequency $$f$$, and wavelength $$\lambda. $$Which of the following correctly relates the wave speed $$v$$?

Accepted Answer

$$v = f \lambda$$

Question 9

A light wave travels from air (n = 1.0) into glass (n = 1.5). What happens to its wavelength and frequency?

Accepted Answer

Wavelength decreases, frequency remains the same.

Question 10

The intensity $$I of a $$spherical wave at a distance $$r$$ from the source is given by $$I = \frac{P}{4\pi r^2$}. If $$you move twice as far from the source, what happens to the intensity?

Accepted Answer

It becomes one-fourth as great.

Question 11

A 100 Hz sound wave travels at 343 m/s. What is the phase difference between two points 0.60 m apart?

Accepted Answer

$$\Delta \phi = 2\pi \frac{0.60}{3.43} = 1.10\ 	ext{rad}$$

Question 12

A solar cell array with an area of $$2.0\ 	ext{m}^2$$ and efficiency of 12% is exposed to sunlight with intensity $$1300\ 	ext{W/m}^2. $$What is the maximum power output?

Accepted Answer

$$P = 0.12 	imes 1300 	imes 2.0 = 312\ 	ext{W}$$

Question 13

The sound intensity level at a rock concert is 120 dB. What is the intensity in $$	ext{W/m}^2$$?

Accepted Answer

$$I = 1.0 	imes 10$$^{0}$$\ 	ext{W/m}^2$$

Question 14

A siren emits a frequency $$f_0. If $$you stand still and the siren moves toward you, what do you hear?

Accepted Answer

A frequency higher than $$f_0.$$

Question 15

A Doppler ultrasound probe emits at 5.0 MHz and detects a maximum frequency shift of 400 Hz from blood flow. If the speed of sound in tissue is 1540 m/s, what is the maximum speed of the blood?

Accepted Answer

$$v = \frac{400}{2 	imes 5.0 	imes 10^6$} 	imes 1540 = 0.062\ 	ext{m/s}$$

Question 16

Which of the following best describes the Doppler effect for light waves from a receding galaxy?

Accepted Answer

The observed wavelength is longer (red shift).

Question 17

A wave travels a distance of one wavelength $$\lambda in $$one period $$T. $$Which equation correctly relates wave speed $$v$$, wavelength $$\lambda$$, and period $$T$$?

Accepted Answer

$$v = \frac{\lambda}{T}$$

Question 18

If the frequency of a sound wave doubles but the speed of sound remains constant, what happens to the wavelength?

Accepted Answer

It is halved.

Chapter 16: Traveling Waves – Physics Study Notes

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