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End of chapter exercises

Choose a word from column B that best describes the concept in column A.

Table 1

Column A

Column B

1. pitch of sound

A. amplitude

2. loudness of sound

B. frequency

3. quality of sound

C. speed

 

D. waveform

Pitch of Sound: Frequency

 

loudness of sound: Amplitude

 

quality of sound: waveform

A tuning fork, a violin string and a loudspeaker are producing sounds. This is because they are all in a state of:

  1. compression

  2. rarefaction

  3. rotation

  4. tension

  5. vibration

What would a drummer do to make the sound of a drum give a note of lower pitch?

  1. hit the drum harder

  2. hit the drum less hard

  3. hit the drum near the edge

  4. loosen the drum skin

  5. tighten the drum skin

e.

loosen the drum skin

What is the approximate range of audible frequencies for a healthy human?

  1. 0,2 Hz 200 Hz

  2. 2 Hz 2000 Hz

  3. 20 Hz 20 000 Hz

  4. 200 Hz 200 000 Hz

  5. 2000 Hz 2 000 000 Hz

e.

20 Hz → 20 000 Hz

X and Y are different wave motions. In air, X travels much faster than Y but has a much shorter wavelength. Which types of wave motion could X and Y be?

Table 2
 

X

Y

1.

microwaves

red light

2.

radio

infra red

3.

red light

sound

4.

sound

ultraviolet

5.

ultraviolet

radio

Astronauts are in a spaceship orbiting the moon. They see an explosion on the surface of the moon. Why can they not hear the explosion?

  1. explosions do not occur in space

  2. sound cannot travel through a vacuum

  3. sound is reflected away from the spaceship

  4. sound travels too quickly in space to affect the ear drum

  5. the spaceship would be moving at a supersonic speed

e.

sound cannot travel through a vacuum

A man stands between two cliffs as shown in the diagram and claps his hands once.

Figure 1
Image

Assuming that the velocity of sound is 330 m·s−1, what will be the time interval between the two loudest echoes?

  1. 2 3 s

  2. 1 6 s

  3. 5 6 s

  4. 1 s

  5. 1 3 s

A dolphin emits an ultrasonic wave with frequency of 0,15 MHz. The speed of the ultrasonic wave in water is 1500 m·s−1. What is the wavelength of this wave in water?

  1. 0,1 mm

  2. 1 cm

  3. 10 cm

  4. 10 m

  5. 100 m

The amplitude and frequency of a sound wave are both increased. How are the loudness and pitch of the sound affected?

Table 3
 

loudness

pitch

A

increased

raised

B

increased

unchanged

C

increased

lowered

D

decreased

raised

E

decreased

lowered

A jet fighter travels slower than the speed of sound. Its speed is said to be:

  1. Mach 1

  2. supersonic

  3. subsonic

  4. hypersonic

  5. infrasonic

A sound wave is different from a light wave in that a sound wave is:

  1. produced by a vibrating object and a light wave is not.

  2. not capable of travelling through a vacuum.

  3. not capable of diffracting and a light wave is.

  4. capable of existing with a variety of frequencies and a light wave has a single frequency.

d.

not capable of traveling through a vacuum.

At the same temperature, sound waves have the fastest speed in:

  1. rock

  2. milk

  3. oxygen

  4. sand

Two sound waves are travelling through a container of nitrogen gas. The first wave has a wavelength of 1,5 m, while the second wave has a wavelength of 4,5 m. The velocity of the second wave must be:

  1. 1 9 the velocity of the first wave.

  2. 1 3 the velocity of the first wave.

  3. the same as the velocity of the first wave.

  4. three times larger than the velocity of the first wave.

  5. nine times larger than the velocity of the first wave.

e.

the same as the velocity of the first wave.

A lightning storm creates both lightning and thunder. You see the lightning almost immediately since light travels at 3 × 108 m·s−1. After seeing the lightning, you count 5 s−1 and then you hear the thunder. Calculate the distance to the location of the storm.

Assuming the speed of sound is 340  ms-1,

 

d=v×t
=340×5
=1700  m

A person is yelling from a second story window to another person standing at the garden gate, 50 m away. If the speed of sound is 344 m·s−1, how long does it take the sound to reach the person standing at the gate?

t=dv
=50344
=0,14  s

Person 1 speaks to person 2. Explain how the sound is created by person 1 and how it is possible for person 2 to hear the conversation.

When person 1 speaks, their vocal chords vibrate, creating identical vibrations in the air. These vibrations, or sound waves, travel through the air and reach person 2. The vibrations in the air causes person 2's eardrums to vibrate and therefore person 2 will hear them.

Sound cannot travel in space. Discuss what other modes of communication astronauts can use when they are outside the space shuttle?

Sound cannot travel in a vacuum. Astronauts may use any other mode of communication that may operate in a vacuum. One method is the use of radios. Radios use electromagnetic waves to send and receive signals and these are able to propagate in a vacuum. If the astronauts' radios fail, they are able to communicate using hand signals.

An automatic focus camera uses an ultrasonic sound wave to focus on objects. The camera sends out sound waves which are reflected off distant objects and return to the camera. A sensor detects the time it takes for the waves to return and then determines the distance an object is from the camera. If a sound wave (speed = 344 m·s−1) returns to the camera 0,150 s after leaving the camera, how far away is the object?

The sound wave travels to the object and back to the camera in 0.15 seconds. Therefore, the distance to the object is:

d=v×t
=344×(0,152)
=25,8  m

Calculate the frequency (in Hz) and wavelength of the annoying sound made by a mosquito when it beats its wings at the average rate of 600 wing beats per second. Assume the speed of the sound waves is 344 m·s−1.

Wavelength:

 

λ=vf
=344600
=0,57  m

 

Frequency:

It beats it wings 600 times per second, therefore the frequency of the sound is 600 Hz.

How does halving the frequency of a wave source affect the speed of the waves?

 The frequency and velocity is independent in homogeneous mediums. Therefore, halving the frequency will not affect the speed of the waves, but it will increase their wavelengths by a factor of 2.

Humans can detect frequencies as high as 20 000 Hz. Assuming the speed of sound in air is 344 m·s−1, calculate the wavelength of the sound corresponding to the upper range of audible hearing.

λ=vf
=34420000
=0,017  m=17  mm

An elephant trumpets at 10 Hz10 Hz. Assuming the speed of sound in air is 344 m·s−1, calculate the wavelength of this infrasonic sound wave made by the elephant.

λ=vf
=34410
=34,4  m

A ship sends a signal out to determine the depth of the ocean. The signal returns 2,5 seconds later. If sound travels at 1450 m·s−1 in sea water, how deep is the ocean at that point?

The sound wave travels to the bottom and back to the ship in 2.5 seconds. Therefore, the distance to the bottom is:

d=v×t
=1450×(2,52)
=1812,5  m

A person shouts at a cliff and hears an echo from the cliff 1 s later. If the speed of sound is 344 m·s−1, how far away is the cliff?

 

The sound wave is heard after 1 s, therefore the soundwave reached the cliff after 0.5s
d=v×t
d=344×0.5
d=172m

Select a word from Column B that best fits the description in Column A:

Table 4

Column A

Column B

1. waves in the air caused by vibrations

A. longitudinal waves

2. waves that move in one direction, but medium moves in another

B. frequency

3. waves and medium that move in the same direction

C. period

4. the distance between consecutive points of a wave which are in phase

D. amplitude

5. how often a single wavelength goes by

E. sound waves

6. half the difference between high points and low points of waves

F. standing waves

7. the distance a wave covers per time interval

G. transverse waves

8. the time taken for one wavelength to pass a point

H. wavelength

 

I. music

 

J. sounds

 

K. wave speed

  1. E. (waves in the air caused by vibrations: sound waves)
  2. G. (waves that move in one direction, but medium moves in another: transverse waves)
  3. H. (the distance between consecutive points of a wave which are in phase: wavelength)
  4. B. (how often a single wavelength goes by: frequency)
  5. D. (half the difference between high points and low points of waves: amplitude)
  6. K. (the distance a wave covers per time interval: wave speed)
  7. C. (the time taken for one wavelength to pass a point: period)