5B2 Sound Flashcards
Describe the properties of sound as a waveform, including characteristics such as pitch and resonance.
Define:
Sound
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.
What type of wave is sound?
Longitudinal
Sound waves vibrate in the same direction as their propagation.
True or False:
Longitudinal waves are also referred to as compression waves.
True
Compression occurs when molecules are pressed together.
Fill in the Blank:
The unit for measuring sound intensity is the ______.
decibel (dB)
The decibel scale is logarithmic, meaning a small increase represents a large change in intensity.
What is the formula to calculate the intensity level of a Sound Wave?
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.
How many times more intense is a 70 dB sound than a 50 dB sound?
100 times more intense.
Each 10 dB increase is a 10-fold increase in intensity:
10^[(70dB−50dB)/10]=100.
True or False:
In compression waves, the areas where particles are pushed close together are called rarefactions.
False
They are called compressions.
Fill in the Blank:
The regions of low particle density in a compression wave are called ______.
Rarefactions
Rarefactions alternate with compressions in longitudinal waves.
Why can’t compression waves travel in a vacuum?
Because they need particles to transfer energy.
In a vacuum, there are no particles to compress or expand.
How do compression and transverse waves differ?
- Compression waves have parallel particle motion.
- Transverse waves have perpendicular particle motion.
M waves are transverse; sound waves are compression.
Fill in the blanks:
The human ear can detect sounds in the range from ____ to _____ Hz.
20; 20,000
Frequencies outside this range may be inaudible to humans.
What are infrasonic sounds?
Sounds with frequencies below 20 Hz.
These are too low for humans to hear.
Fill in the Blank:
Sounds with frequencies above 20,000 Hz are called ______.
ultrasonic
Ultrasonic waves are commonly used in medical imaging.
Define:
Speed of sound
The rate at which sound waves travel through a medium.
In air at 20°C, the speed is approximately 343 m/s.
True or False:
Sound travels faster in water than in air.
True
Water molecules are more densely packed than air, facilitating faster sound propagation.
Name three factors that affect the speed of sound.
- Medium type
- Temperature
- Pressure
Solids typically conduct sound faster than gases.
What are factors that do not affect the speed of sound?
- Pressure
- Amplitude
Sound speed depends on factors like temperature, medium type, and density, but not on pressure or amplitude.
Fill in the Blank:
The speed of sound in water is approximately ____ m/s at 20°C.
1480
This is faster than in air due to water’s higher density.
What is a sonic boom?
A loud noise produced when an object moves faster than the speed of sound, creating shock waves.
Supersonic jets often cause sonic booms.
True or False:
The sound barrier refers to the speed beyond which sound waves cannot travel.
False
The sound barrier refers to the resistance experienced as an object approaches the speed of sound.
Why does sound travel faster in solids than in gases?
Because particles in solids are more tightly packed, allowing faster transmission of vibrations.
Metals like steel conduct sound efficiently.
True or False:
A shock wave is formed when an object travels slower than the speed of sound.
False
Shock waves only form when an object exceeds the speed of sound.
Fill in the blank:
The speed of sound in air increases by approximately ____ m/s per degree Celsius rise in temperature.
0.6
This relationship holds under normal atmospheric conditions.
How far is a lightning strike if the delay between the flash and the thunder is 3 seconds?
Approximately 1 kilometer away.
Sound travels roughly 343 m/s in air, so (343m/s)×(3s)≈1029 m.
What is sound refraction?
The bending of waves when parts of the wavefront travel at different speeds.
This can occur with varying wind conditions or air temperatures. Changes in medium properties, like temperature or wind, affect sound speed and cause refraction.
Explain how temperature variations near the ground affect the propagation of sound.
Warmer air near the ground increases the speed of sound, causing sound waves to bend away from the surface.
This effect is called refraction, where sound waves change direction due to speed variations.
Define:
Echo
The reflection of a sound wave when it bounces back from a surface.
The reflected sound must travel more than 17 meters from the source to be distinguishable as an echo.
Why must a surface be at least 17 meters away to hear an echo?
Because sound must travel 17 meters round trip in 0.1 seconds for the echo to be heard.
Echoes need a 0.1 s delay; 343 m/s × 0.1 s = 34 m (17 m each way).
What is reverberation?
When sound waves reflect multiple times, blending with the original sound.
It is common in enclosed spaces with reflective surfaces.
True or False:
Concert halls are designed to control reverberation for optimal sound clarity.
True
Excessive reverberation reduces clarity, while well-managed reverberation enhances the listening experience.
Define:
Pitch
in sound
The perception of how high or low a sound is, determined by its frequency.
Higher frequencies correspond to higher pitch.
What is loudness in sound?
The perception of the intensity or energy of a sound.
Loudness is related to amplitude and measured in decibels (dB).
True or False:
Frequency determines the loudness of a sound.
False
Frequency determines pitch, not loudness.
Why do louder sounds cause more discomfort to human ears?
Louder sounds carry more energy and can damage the sensitive hair cells in the cochlea.
Prolonged exposure to high-decibel sounds can cause hearing loss.
True or False:
Pitch and frequency are directly proportional.
True
Higher frequency results in higher pitch perception.
Define:
beats
in sound waves
Periodic variations in sound intensity caused by the interference of two waves with slightly different frequencies.
The difference in frequency determines the beat frequency.
What causes the alternating loud and soft pattern of beats?
Constructive interference creates loud sounds, and destructive interference creates soft sounds.
This alternating pattern forms the beat frequency.
How is the beat frequency calculated?
By subtracting the lower frequency from the higher frequency.
f beat =|f1-f2|
If two sound waves have frequencies of 256 Hz and 260 Hz, what is the beat frequency?
4 Hz
The beat frequency is the absolute difference between the two frequencies.
Why are beats useful in tuning musical instruments?
They help identify when two notes are perfectly in tune by eliminating the beat frequency.
When there are no beats, the frequencies match.
Define:
resonance
in sound waves
It occurs when an object vibrates at its natural frequency due to a matching external sound frequency.
This amplifies the sound wave.
Name two factors that determine the natural frequency of an object.
- Shape
- Material
The natural frequency depends on physical properties like stiffness and mass distribution.
True or False:
Resonance only happens in musical instruments.
False
Resonance can occur in pipes, bridges, and even vocal cords.
Why does a tuning fork placed near a resonating box sound louder?
The box amplifies the sound by resonating at the same frequency as the tuning fork.
This increases the sound intensity.
What role does resonance play in a guitar string?
When a string vibrates, the body of the guitar resonates, amplifying the sound.
The air inside the body also contributes to the resonance.
Fill in the blank:
In an open pipe, resonance occurs when the pipe length matches a multiple of ______ the wavelength.
Half
This creates constructive interference.
How does resonance behavior differ in open versus closed pipes?
- Open pipes resonate at half-wavelength intervals.
- Closed pipes resonate at odd quarter-wavelength intervals.
This difference affects pitch and harmonics.
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?
100 Hz
Use f = v/4L, since a closed pipe supports a quarter-wavelength at the fundamental.
Why is resonance important in wind instruments like flutes?
It allows the air column inside the instrument to vibrate at specific frequencies, producing distinct notes.
This enhances the sound quality.
Why does an ambulance siren sound higher-pitched as it approaches you and lower-pitched as it moves away?
As the ambulance approaches, sound waves are compressed, increasing the frequency. As it moves away, the waves stretch, lowering the frequency.
This is an example of the Doppler effect. This compression and stretching of waves create pitch changes.
Fill in the Blank:
The Doppler effect is useful for _____ _____ to measure the speed of vehicles.
Radar systems
Police use this technology for speed detection.
How is the Doppler effect used in emergency medical diagnostics?
Ultrasounds detect blood flow abnormalities by analyzing frequency shifts in reflected sound waves.
This helps diagnose blockages or abnormal blood flow.
What does sonar do?
It measures the time taken for sound waves to travel and reflect back, calculating distances underwater.
Sonar systems can use either ultrasonic or audible frequencies.
Why is the Doppler effect important for submarines?
It helps detect and track moving objects underwater using sonar signals.
Frequency shifts indicate the speed and direction of targets.
Why do you hear only one radio station at a time instead of all simultaneously?
The radio tunes to a specific frequency and rejects all others.
This is achieved through a process called frequency filtering.
How does a radio wave differ from a sound wave?
- Radio waves are electromagnetic.
- Sound waves are mechanical.
Radio waves can travel through a vacuum; sound waves require a medium.
