5B2 Sound

Question 1

Define:

Sound

Answer 1

Vibrations that travel through a medium (such as air, water, or solids) and are perceived by the ear.

Sound requires a medium for propagation, unlike electromagnetic waves.

Question 2

What type of wave is sound?

Answer 2

Longitudinal

Sound waves vibrate in the same direction as their propagation.

Question 3

True or False:

Longitudinal waves are also referred to as compression waves.

Answer 3

True

Compression occurs when molecules are pressed together.

Question 4

Fill in the Blank:

The unit for measuring sound intensity is the ______.

Answer 4

decibel (dB)

The decibel scale is logarithmic, meaning a small increase represents a large change in intensity.

Question 5

What is the formula to calculate the intensity level of a Sound Wave?

Answer 5

dB=10×log₁₀=(I/I₀)

I is the measured intensity; I₀ is the reference (typically 10⁻¹² W/m²). The formula compresses a wide range of sound levels.

Question 6

How many times more intense is a 70 dB sound than a 50 dB sound?

Answer 6

100 times more intense.

Each 10 dB increase is a 10-fold increase in intensity:
10^[(70dB−50dB)/10]=100.

Question 7

True or False:

In compression waves, the areas where particles are pushed close together are called rarefactions.

Answer 7

False

They are called compressions.

Question 8

Fill in the Blank:

The regions of low particle density in a compression wave are called ______.

Answer 8

Rarefactions

Rarefactions alternate with compressions in longitudinal waves.

Question 9

Why can’t compression waves travel in a vacuum?

Answer 9

Because they need particles to transfer energy.

In a vacuum, there are no particles to compress or expand.

Question 10

How do compression and transverse waves differ?

Answer 10

• Compression waves have parallel particle motion.
• Transverse waves have perpendicular particle motion.

M waves are transverse; sound waves are compression.

Question 11

Fill in the blanks:

The human ear can detect sounds in the range from ____ to _____ Hz.

Answer 11

20; 20,000

Frequencies outside this range may be inaudible to humans.

Question 12

What are infrasonic sounds?

Answer 12

Sounds with frequencies below 20 Hz.

These are too low for humans to hear.

Question 13

Fill in the Blank:

Sounds with frequencies above 20,000 Hz are called ______.

Answer 13

ultrasonic

Ultrasonic waves are commonly used in medical imaging.

Question 14

Define:

Speed of sound

Answer 14

The rate at which sound waves travel through a medium.

In air at 20°C, the speed is approximately 343 m/s.

Question 15

True or False:

Sound travels faster in water than in air.

Answer 15

True

Water molecules are more densely packed than air, facilitating faster sound propagation.

Question 16

Name three factors that affect the speed of sound.

Answer 16

1. Medium type
2. Temperature
3. Density

Solids typically conduct sound faster than gases due to higher density and elasticity.

Question 17

What are factors that do not affect the speed of sound?

Answer 17

1. Pressure (in gases at constant temperature)
2. Amplitude

Sound speed depends on factors like temperature, medium type, and density, but not on pressure or amplitude.

Question 18

Fill in the Blank:

The speed of sound in water is approximately ____ m/s at 20°C.

Answer 18

1480

This is faster than in air due to water’s higher density.

Question 19

What is a sonic boom?

Answer 19

A loud noise produced when an object moves faster than the speed of sound, creating shock waves.

Supersonic jets often cause sonic booms.

Question 20

True or False:

The sound barrier refers to the speed beyond which sound waves cannot travel.

Answer 20

False

The sound barrier refers to the resistance experienced as an object approaches the speed of sound.

Question 21

Why does sound travel faster in solids than in gases?

Answer 21

Because particles in solids are more tightly packed, allowing faster transmission of vibrations.

Metals like steel conduct sound efficiently.

Question 22

True or False:

A shock wave is formed when an object travels slower than the speed of sound.

Answer 22

False

Shock waves only form when an object exceeds the speed of sound.

Question 23

Fill in the blank:

The speed of sound in air increases by approximately ____ m/s per degree Celsius rise in temperature.

Answer 23

0.6

This relationship holds under normal atmospheric conditions.

Question 24

How far is a lightning strike if the delay between the flash and the thunder is 3 seconds?

Answer 24

Approximately 1 kilometer away.

Sound travels roughly 343 m/s in air, so (343m/s)×(3s)≈1029 m.

Question 25

What is **sound refraction**?

Answer 25

The **bending of waves** when parts of the wavefront travel at different speeds. ## Footnote This can occur with varying wind conditions or air temperatures. Changes in medium properties, like temperature or wind, affect sound speed and cause refraction.

Question 26

Explain how **temperature variations** near the ground affect the propagation of sound.

Answer 26

Warmer air near the ground increases the speed of sound, causing sound waves to **bend away** from the surface. ## Footnote This effect is called **refraction**, where sound waves change direction due to speed variations.

Question 27

# Define: Echo

Answer 27

The **reflection of a sound wave** when it bounces back from a surface. ## Footnote The reflected sound must travel more than 17 meters from the source to be distinguishable as an echo.

Question 28

Why must a surface be **at least 17 meters away** to hear an echo?

Answer 28

Because **sound must travel 17 meters round trip in 0.1 seconds** for the echo to be heard. ## Footnote Echoes need a 0.1 s delay; 343 m/s × 0.1 s = 34 m (17 m each way).

Question 29

What is **reverberation**?

Answer 29

When **sound waves reflect multiple times**, blending with the original sound. ## Footnote It is common in enclosed spaces with reflective surfaces.

Question 30

# True or False: **Concert halls** are designed to **control reverberation** for optimal sound clarity.

Answer 30

True ## Footnote Excessive reverberation reduces clarity, while well-managed reverberation enhances the listening experience.

Question 31

# Define: Pitch | in sound

Answer 31

The **perception of how high or low a sound is**, determined by its frequency. ## Footnote Higher frequencies correspond to higher pitch.

Question 32

What is **loudness** in sound?

Answer 32

The **perception of the intensity** or energy of a sound. ## Footnote Loudness is related to amplitude and measured in **decibels (dB)**.

Question 33

# True or False: Frequency determines the **loudness** of a sound.

Answer 33

False ## Footnote Frequency determines pitch, not loudness.

Question 34

Why do **louder sounds** cause more discomfort to human ears?

Answer 34

Louder sounds **carry more energy and can damage the sensitive hair cells** in the cochlea. ## Footnote Prolonged exposure to high-decibel sounds can cause hearing loss.

Question 35

# True or False: **Pitch and frequency** are directly proportional.

Answer 35

True ## Footnote Higher frequency results in higher pitch perception.

Question 36

# Define: beats | in sound waves

Answer 36

**Periodic variations in sound intensity** caused by the interference of two waves with slightly different frequencies. ## Footnote The difference in frequency determines the beat frequency.

Question 37

What causes the alternating **loud and soft** pattern of beats?

Answer 37

**Constructive interference** creates loud sounds, and **destructive interference** creates soft sounds. ## Footnote This alternating pattern forms the beat frequency.

Question 38

How is the beat **frequency calculated**?

Answer 38

By **subtracting the lower frequency** from the higher frequency. ## Footnote f beat =|f1-f2|

Question 39

If two sound waves have frequencies of **256 Hz and 260 Hz**, what is the beat frequency?

Answer 39

4 Hz ## Footnote The beat frequency is the **absolute difference** between the two frequencies.

Question 40

Why are beats useful in tuning **musical instruments**?

Answer 40

They help identify when **two notes are perfectly** in tune by eliminating the beat frequency. ## Footnote When there are no beats, the frequencies match.

Question 41

# Define: resonance | in sound waves

Answer 41

It occurs when an **object vibrates at its natural frequency** due to a matching external sound frequency. ## Footnote This amplifies the sound wave.

Question 42

Name two factors that determine the **natural frequency** of an object.

Answer 42

1. Shape 2. Material ## Footnote The natural frequency depends on physical properties like stiffness and mass distribution.

Question 43

# True or False: Resonance only happens in **musical instruments**.

Answer 43

False ## Footnote Resonance can occur in pipes, bridges, and even vocal cords.

Question 44

Why does a **tuning fork** placed near a resonating box sound louder?

Answer 44

The box **amplifies the sound by resonating** at the same frequency as the tuning fork. ## Footnote This increases the sound intensity.

Question 45

What role does **resonance** play in a **guitar string**?

Answer 45

When a string vibrates, the body of the guitar resonates, amplifying the sound. ## Footnote The air inside the body also contributes to the resonance.

Question 46

# Fill in the blank: In an **open pipe**, resonance occurs when the pipe length matches a multiple of \_\_\_\_\_\_ the wavelength.

Answer 46

Half ## Footnote This creates constructive interference.

Question 47

How does resonance behavior differ in **open versus closed pipes**?

Answer 47

* Open pipes resonate at **half-wavelength intervals**. * Closed pipes resonate at **odd quarter-wavelength intervals**. ## Footnote This difference affects pitch and harmonics.

Question 48

A closed pipe has a length of **0.85 m**. If the speed of sound is **340 m/s**, what is the frequency of the **fundamental resonance**?

Answer 48

100 Hz ## Footnote Use f = v/4L, since a closed pipe supports a quarter-wavelength at the fundamental.

Question 49

Why is resonance important in **wind instruments** like flutes?

Answer 49

It allows the air column inside the instrument to **vibrate at specific frequencies**, producing distinct notes. ## Footnote This enhances the sound quality.

Question 50

Why does an **ambulance siren** sound higher-pitched as it approaches you and lower-pitched as it moves away?

Answer 50

As the ambulance approaches, sound **waves are compressed**, increasing the frequency. As it moves away, the **waves stretch**, lowering the frequency. ## Footnote This is an example of the Doppler effect. This compression and stretching of waves create pitch changes.

Question 51

# Fill in the Blank: The Doppler effect is useful for \_\_\_\_\_ \_\_\_\_\_ to measure the **speed of vehicles**.

Answer 51

Radar systems ## Footnote Police use this technology for speed detection.

Question 52

How is the **Doppler effect** used in **emergency medical diagnostics**?

Answer 52

Ultrasounds **detect blood flow abnormalities** by analyzing frequency shifts in reflected sound waves. ## Footnote This helps diagnose blockages or abnormal blood flow.

Question 53

What does **sonar** do?

Answer 53

It measures the time taken for sound waves to travel and reflect back, **calculating distances underwater**. ## Footnote Sonar systems can use either ultrasonic or audible frequencies.

Question 54

Why is the **Doppler effect** important for **submarines**?

Answer 54

It helps detect and **track moving objects underwater using sonar** signals. ## Footnote Frequency shifts indicate the speed and direction of targets.

Question 55

Why do you hear only one **radio station** at a time instead of all simultaneously?

Answer 55

The radio tunes to a **specific frequency** and rejects all others. ## Footnote This is achieved through a process called **frequency filtering**.

Question 56

How does a **radio wave** differ from a **sound wave**?

Answer 56

* Radio waves are **electromagnetic**. * Sound waves are **mechanical**. ## Footnote Radio waves can travel through a vacuum; sound waves require a medium.