Correct option: (B).

Sound is produced by vibrating objects. Vibration is a periodic to-and-fro motion about a mean position.

Correct option: (B).

The vocal cords are stretched muscular flaps inside the larynx or voice box.

Correct option: (C).

Correct option: (B).

Correct option: (D).

Sound is a mechanical wave and needs particles of a material medium to transfer the disturbance.

Correct option: (A).

Air particles vibrate parallel to the direction in which the sound wave propagates.

Correct option: (B).

Correct option: (B).

Correct option: (B).

It is the disturbance and energy that propagate; the particles themselves oscillate locally.

Correct option: (B).

Correct option: (B).

Correct option: (B).

Correct option: (A).

A loudspeaker uses electrical signals to make its cone or diaphragm vibrate and produce sound.

Correct option: (C).

Correct option: (B).

Correct option: (C).

Correct option: (A).

Correct option: (B).

Correct option: (A).

Correct option: (C).

Correct option: (C).

The chapter gives the general order: solids > liquids > gases.

Correct option: (A).

The chapter also notes that increasing humidity increases the speed of sound in air.

Correct option: (A).

Higher frequency is generally perceived as higher pitch.

Correct option: (B).

Correct option: (C).

35 kHz is above 20 kHz.

Correct option: (B).

Correct option: (A).

Correct option: (D).

An octave corresponds to doubling the fundamental frequency.

The sound must make a round trip in at least 0.1 s.

Correct option: (B).

Correct option: (B).

Sound is heard while the stretched rubber band is vibrating. When the vibration stops, the sound also stops.

Hence, the activity supports the conclusion that sound is produced by vibrations.

When a struck tuning fork is touched gently to the water surface, the vibrating prong produces visible disturbances or waves in the water.

This provides visible evidence that the prongs are vibrating while producing sound.

Solid: Knocking a desk can be heard clearly when the ear is placed against the desk.

Liquid: Metal spoons struck while submerged in water can still be heard.

As air is removed from the bell jar, the sound of the ringing bell becomes progressively fainter even though the bell can still be seen vibrating.

This shows that sound requires a material medium and cannot propagate through vacuum.

Compression: region of higher-than-average density where particles are relatively closer together.

Rarefaction: region of lower-than-average density where particles are relatively farther apart.

No.

The particles oscillate about their own mean positions. The sequence of compressions and rarefactions, and therefore the energy, travels through the medium.

1 minute = 60 s.

Distance between successive compressions equals one wavelength.

Increasing order:

Sound travels about 4.4 times faster in water than in air using these values.

Pitch: human perception associated mainly with frequency. Higher frequency generally gives higher pitch.

Loudness: subjective perception associated mainly with amplitude. Larger amplitude is generally heard as a louder sound.

Intensity is a physically measurable rate of sound-energy flow per unit area.

Loudness is a subjective perception and depends partly on the hearing ability of the listener.

• Infrasonic: below 20 Hz.
• Audible: approximately 20 Hz to 20,000 Hz.
• Ultrasonic: above 20,000 Hz or 20 kHz.

Echo: a reflected sound heard separately from the original, typically when the time gap is at least about 0.1 s.

Reverberation: persistence of sound caused by multiple reflections arriving so quickly that they overlap with one another.

Microphone: sound energy → electrical signal.

Speaker: electrical signal → vibration of diaphragm/cone → sound energy.

Answer: 1200 oscillations.

20 Hz:

20 kHz = 20,000 Hz:

The travel time of light is negligible for this estimate.

Through air:

Through steel:

Since the time gap is far greater than 0.1 s, the arrivals can be distinguished separately.

At 0°C:

At 22°C:

Approximately 0.20 s extra.

Depth = 3.0 km.

Total distance:

When frequency doubles while speed remains constant, wavelength becomes half.

Sound spreads outward over an increasingly larger area.

The available wave energy is therefore distributed over a larger area, so the sound energy crossing each unit area per unit time decreases.

Tone: nearly single-frequency sound.

Musical note: combination of a fundamental frequency and higher overtones.

Timbre: characteristic quality that allows different instruments to sound different even when playing the same note at similar loudness.

1. Sound entering the ear causes the eardrum to vibrate.
2. Tiny bones amplify and transmit the vibrations.
3. The cochlea converts them into electrical signals.
4. These signals travel to the brain, which interprets them as sound.

Ultrasonic applications include:

• ultrasonography,
• breaking kidney stones,
• detecting defects inside metal blocks,
• ultrasonic cleaning or welding,
• SONAR and echolocation.

Infrasonic applications include:

• detecting earthquakes,
• monitoring volcanic activity,
• detecting severe storms over long distances.

1. An electric bell is placed inside a bell jar and switched on.
2. With air present, the bell is clearly heard.
3. A vacuum pump gradually removes air from the jar.
4. The sound becomes progressively fainter even though the bell continues vibrating visibly.
5. When a near vacuum is produced, almost no sound is heard.
6. When air is allowed back into the jar, the sound becomes louder again.

The vibrating source remains active, but sound transmission decreases as the number of particles in the medium decreases. Hence a material medium is necessary for sound propagation.

When one end of a stretched slinky is repeatedly pushed and pulled, alternating regions of closely spaced and widely spaced turns appear.

These are analogous to compressions and rarefactions in air.

A marked turn of the slinky does not travel to the opposite end. Instead, it moves back and forth about its original position while the disturbance travels along the slinky.

Similarly, air particles oscillate parallel to the direction of propagation, while the sound disturbance and energy move forward.

• The horizontal axis represents distance from the source.
• The vertical axis represents density of the medium.
• The dashed central level represents average density.
• A crest represents maximum density and corresponds to a compression.
• A trough represents minimum density and corresponds to a rarefaction.
• Wavelength is the distance between two consecutive crests or two consecutive troughs.
• Amplitude is the maximum density change above or below the average value.

Sound is a mechanical wave and requires particles to transfer compressions and rarefactions. Therefore it cannot travel through vacuum.

Light is not a mechanical wave and can propagate through vacuum.

In one complete time period T, a particular phase of the wave such as a crest travels one wavelength λ.

Since:

therefore:

Thus speed equals wavelength multiplied by frequency.

Wave A:

Wave B:

Wave B has twice the frequency and therefore would generally be perceived as having the higher pitch.

Answers: 100 Hz, 0.01 s, 3000 oscillations.

These ratios illustrate the chapter’s general statement that sound travels fastest in solids, slower in liquids and slowest in gases.

For equal round-trip distance:

If:

then:

An echo is a reflected sound heard distinctly after the original sound, usually when the time separation is at least about 0.1 s.

Reverberation is the persistence of sound due to repeated reflections arriving too quickly to be heard separately.

Excess reverberation makes speech and music unclear. It can be controlled by using sound-absorbing materials such as:

• curtains,
• upholstered chairs,
• soft porous wall or ceiling panels.

Good auditorium design preserves useful reflection while reducing unwanted multiple reflections.

Frequency:

Wavelength:

Round-trip distance:

Wavelength:

Distance:

SONAR sends ultrasonic sound waves through water. These waves reflect from an underwater object and return to a detector.

By analysing the reflected sound, the system can determine properties such as the object’s distance and direction.

The recorded time represents the journey:

Therefore the one-way distance is:

Prolonged exposure to high sound levels may affect health, sleep and hearing, and can lead to hearing loss.

A hearing aid generally includes:

• a microphone to capture sound,
• an amplifier to strengthen the electrical signal,
• a speaker to reproduce the amplified sound for the user.

Reducing unnecessary exposure to loud sound is therefore important for protecting hearing.

For constant v:

Therefore:

At 500 Hz:

At 1000 Hz:

Frequency doubles and wavelength halves. The speed remains essentially fixed because the medium and conditions are unchanged.

Music contains many frequencies produced simultaneously.

If those frequencies travelled at substantially different speeds, they would arrive at a distant listener at different times. The timing and relation between the components of the musical sound would be altered.

Ordinary air does not show this large frequency-dependent speed variation under the conditions discussed in the chapter, so musical sounds preserve their temporal relationship much better.

Next crest:

A trough occurs halfway between consecutive crests:

The amplitude remains 3 density units above or below the average-density line.

Yes.

Intensity is a measurable physical property of the sound wave at that location. Loudness is a subjective perception that also depends on the listener’s hearing sensitivity.

Thus the same physical intensity may not necessarily produce exactly the same perceived loudness for every person.

The minimum echo distance rises slightly because sound travels farther during the same 0.1 s interval.

Approximately 0.20 s extra.

Water:

Steel:

One octave:

Two octaves:

Three octaves:

50 kHz is above the upper human hearing limit of approximately 20 kHz, so the sound is ultrasonic for humans.

The burst is seen almost immediately because light travels enormously faster than sound over this distance.

Therefore the interval between seeing the flash/burst and hearing the sound is a good approximation to the sound travel time.

(a) Wavelength in air:

(b) Time period:

(c) Distance of wall:

(d) Wavelength in water:

(e) Explanation:

The frequency is fixed by the vibrating source. When the sound enters a different medium, its speed changes. Since:

the wavelength adjusts to the new speed while the source frequency remains unchanged.