Sound

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課程筆記

What is Sound?

Sound is produced by a vibrating object.
The vibration transfers energy by making air particles collide.
Sound is a longitudinal wave: vibrations are parallel to the direction of wave travel.

Compressions and Rarefactions

Compressions are regions where air particles are close together.
Rarefactions are regions where air particles are further apart.
The wavelength is the distance between two consecutive compressions (or two rarefactions).

Frequency and Pitch

Frequency is the number of waves passing a point per second, measured in Hertz (Hz).
The higher the frequency, the higher the pitch.
Human auditory range: 20 Hz to 20,000 Hz.
Sound above 20,000 Hz is called ultrasound.

Amplitude and Volume

Amplitude is the maximum displacement of particles from their rest position.
The larger the amplitude, the louder the sound.

Detecting Sound

A microphone converts sound waves into electrical signals.
The electrical signal can be displayed on an oscilloscope.
The human ear works similarly: sound vibrates the eardrum, which sends electrical signals to the brain.

Diagram showing reflection of a sound wave (not to scale; sound reflects similarly to light).

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練習題

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1.What causes a sound wave?
Easy
- AA vibrating object
- BA stationary object
- CLight energy
- DHeat energy
2.Which type of wave is a sound wave?
Easy
- ALongitudinal
- BTransverse
- CElectromagnetic
- DStationary
3.What is the frequency of a sound wave measured in?
Easy
- AHertz (Hz)
- BDecibels (dB)
- CMetres (m)
- DSeconds (s)
4.The human auditory range is 20 Hz to 20 000 Hz. How many waves pass a point every second for a sound wave with a frequency of 20 000 Hz?
Easy
- A20 000
- B20
- C200
- D2 000
5.Which statement about compressions and rarefactions is correct?
Easy
- AA compression is where air particles are close together; a rarefaction is where they are further apart.
- BA compression is where air particles are further apart; a rarefaction is where they are close together.
- CA compression and rarefaction are the same.
- DA compression is a region of low pressure; a rarefaction is a region of high pressure.
6.Which of the following statements is true?
Easy
- AA microphone turns a sound wave into an electrical signal.
- BA microphone turns an electrical signal into a sound wave.
- CA microphone amplifies a sound wave.
- DA microphone increases the frequency of a sound wave.
7.The wavelength of a sound wave is the distance between:
Easy
- AOne compression and the next compression
- BA compression and a rarefaction
- CThe source and the observer
- DThe highest and lowest point of the wave
8.A sound wave has a frequency of 440 Hz. How many complete waves pass a point in 0.5 seconds?
Medium
- A220
- B440
- C880
- D110

更多題目

9.Which property of a sound wave is related to its loudness?
Easy
- AAmplitude
- BFrequency
- CWavelength
- DSpeed
10.An oscilloscope trace shows two sound waves with the same amplitude but different frequencies. Which wave has the higher pitch?
Easy
- AThe wave with more cycles in the same time
- BThe wave with fewer cycles in the same time
- CThe wave with larger amplitude
- DThe wave with smaller amplitude
11.Sound waves cannot travel through:
Easy
- AA vacuum
- BAir
- CWater
- DSteel
12.A sound wave in air has a wavelength of 0.5 m and a speed of 340 m/s. What is its frequency?
Medium
- A680 Hz
- B170 Hz
- C340 Hz
- D850 Hz
13.A sound wave in air has a frequency of 256 Hz and a wavelength of 1.33 m. What is the speed of the sound wave?
Medium
- A340 m/s
- B192 m/s
- C256 m/s
- D1.33 m/s
14.A student uses a microphone and an oscilloscope to display a sound wave. The trace shows a wave with a small amplitude. What does this indicate about the sound?
Easy
- AThe sound has a low pitch.
- BThe sound is quiet.
- CThe sound has a high frequency.
- DThe sound is loud.
15.An oscilloscope trace shows two sound waves. Wave A has a frequency of 440 Hz and Wave B has a frequency of 880 Hz. Which statement is correct?
Easy
- AWave A has a higher pitch than Wave B.
- BWave B has a higher pitch than Wave A.
- CBoth waves have the same pitch.
- DWave A is louder than Wave B.
16.A sound wave travels 680 m in 2 seconds. What is the speed of the sound wave?
Medium
- A340 m/s
- B1360 m/s
- C680 m/s
- D170 m/s
17.A sound wave has a speed of 340 m/s and a wavelength of 0.85 m. What is its frequency?
Medium
- A400 Hz
- B289 Hz
- C340 Hz
- D0.0025 Hz
18.The table shows the speed of sound in different materials. In which material does sound travel fastest? Material | Speed (m/s) Air | 340 Water | 1500 Steel | 5000 Rubber | 60
Easy
- AAir
- BWater
- CSteel
- DRubber
19.A student claps their hands 100 m from a wall. They hear the echo 0.6 s later. What is the speed of sound in air?
Medium
- A333 m/s
- B167 m/s
- C60 m/s
- D600 m/s
20.A sound wave is displayed on an oscilloscope. The time base is set to 2 ms per division. One complete wave spans 5 divisions. What is the frequency of the sound wave?
Hard
- A100 Hz
- B200 Hz
- C50 Hz
- D10 Hz
21.Which of the following is a longitudinal wave?
Easy
- ALight wave
- BSound wave
- CWater wave
- DRadio wave
22.What is the unit of frequency?
Easy
- AMetre
- BHertz
- CSecond
- DDecibel
23.A sound wave has a frequency of 500 Hz. How many compressions pass a point in 2 seconds?
Medium
- A250
- B500
- C1000
- D200
24.A student measures the speed of sound using an echo method. They stand 85 m from a wall and record the time for an echo as 0.5 s. What is the speed of sound?
Medium
- A340 m/s
- B170 m/s
- C42.5 m/s
- D85 m/s
25.A student uses a microphone connected to an oscilloscope to display a sound wave. The time base of the oscilloscope is set to 2 ms per division. One complete wave spans 4 divisions. What is the frequency of the sound?
Hard
- A125 Hz
- B250 Hz
- C500 Hz
- D2000 Hz
26.A student stands 170 m from a tall wall and claps their hands. They hear the echo 1.0 s later. What is the speed of sound in air?
Medium
- A170 m/s
- B340 m/s
- C85 m/s
- D680 m/s
27.Which of the following is the correct unit for frequency?
Easy
- AHertz (Hz)
- BMetres per second (m/s)
- CMetres (m)
- DSeconds (s)
28.The table shows the speed of sound in different materials. In which material does sound travel fastest? Material | Speed (m/s) Air | 340 Water | 1500 Steel | 5000
Easy
- AAir
- BWater
- CSteel
- DSpeed is same in all
29.A sound wave is displayed on an oscilloscope. The time base is set to 2 ms per division. One complete wave spans 5 divisions. What is the frequency of the sound?
Hard
- A100 Hz
- B200 Hz
- C400 Hz
- D1000 Hz
30.Which of the following best describes a longitudinal wave?
Easy
- AVibrations are parallel to the direction of wave travel
- BVibrations are perpendicular to the direction of wave travel
- CVibrations are circular
- DVibrations are random
31.Frequency is defined as:
Easy
- AThe number of waves passing a point per second
- BThe distance between two consecutive compressions
- CThe height of a wave from its rest position
- DThe speed of the wave
32.How many waves pass a point every second for an ultrasound wave with a frequency of 20 000 Hz?
Easy
- A20 000
- B200
- C20
- D2
33.What is the difference between a compression and a rarefaction in a sound wave?
Easy
- AIn a compression, particles are close together; in a rarefaction, particles are further apart
- BIn a compression, particles are further apart; in a rarefaction, particles are close together
- CCompressions are high frequency, rarefactions are low frequency
- DCompressions are loud, rarefactions are quiet
34.True or false: The higher the frequency of a sound wave, the louder it is.
Medium
- AFalse
- BTrue
- CTrue only for low frequencies
- DFalse only for high frequencies
35.True or false: The lower the amplitude of a sound wave, the quieter it is.
Medium
- ATrue
- BFalse
- CTrue only for high frequencies
- DFalse only for low frequencies
36.What device is used to convert a sound wave into an electrical signal?
Easy
- AMicrophone
- BOscilloscope
- CLoudspeaker
- DEar drum
37.On an oscilloscope trace, two sound waves have the same amplitude but different frequencies. Which wave has the higher pitch?
Medium
- AThe wave with more cycles per unit time
- BThe wave with larger amplitude
- CThe wave with fewer cycles per unit time
- DThe wave with smaller amplitude
38.A sound wave travels in air. Which of the following correctly describes the movement of air particles as the wave passes?
Easy
- AParticles vibrate parallel to the direction of wave travel
- BParticles vibrate perpendicular to the direction of wave travel
- CParticles are carried along with the wave
- DParticles remain stationary
39.Which of the following is NOT true about sound waves?
Easy
- AThey can travel through a vacuum
- BThey are longitudinal waves
- CThey transfer energy
- DThey require a medium to travel
40.A student claps their hands 170 m from a tall wall. They hear the echo 1.0 s later. What is the speed of sound in air?
Medium
- A340 m/s
- B170 m/s
- C85 m/s
- D680 m/s
41.Sound waves are longitudinal waves.
Easy
True or false?
42.The frequency of a sound wave is measured in meters per second.
Easy
True or false?
43.Compressions are regions where air particles are far apart.
Easy
True or false?
44.A larger amplitude of a sound wave corresponds to a louder sound.
Easy
True or false?
45.The wavelength of a sound wave is the distance between a compression and the next rarefaction.
Medium
True or false?
46.A microphone converts sound waves into electrical signals.
Easy
True or false?
47.Match each term with its correct description.
Medium
- Compression
- Rarefaction
- Wavelength
- Frequency
- Distance between two compressions
- Region where particles are close together
- Number of waves per second
- Region where particles are far apart
48.Arrange the following steps in the correct order for how sound is heard by a human ear.
Medium
- Sound waves vibrate the eardrum
- Eardrum vibrations are converted into electrical signals
- Electrical signals are sent to the brain
- Brain interprets the signals as sound
49.Which of the following statements about sound waves are true? (Select all that apply)
Medium
- ASound waves are transverse waves
- BSound waves are longitudinal waves
- CSound waves can travel through a vacuum
- DSound waves transfer energy
- ESound waves are caused by vibrations
50.The amplitude of a sound wave is related to its loudness.
Easy
True or false?
51.Complete the sentence.
Easy
Sound is produced by a(n) ____ object.
52.A sound wave has a frequency of 440 Hz. What does this mean?
Easy
53.A sound wave has a speed of 340 m/s and a frequency of 680 Hz. What is its wavelength? Give your answer in metres.
Medium
54.Complete the sentences.
Medium
Sound waves are ____ waves. The vibrations are ____ to the direction of wave travel.
55.A sound wave has a speed of 340 m/s and a frequency of 680 Hz. What is its wavelength? Give your answer in metres.
Medium
- A2.5 m
- B-0.5 m
- C0.5 m
- D1.5 m

複習筆記

## Sound Waves - **Cause**: Sound waves are produced by **vibrating objects**. The vibration transfers energy through air particles. - **Type**: Sound is a **longitudinal wave** – vibrations are **parallel** to the direction of wave travel. ### Wave Structure - **Compressions**: Regions where air particles are close together. - **Rarefactions**: Regions where air particles are spread apart. - **Wavelength**: Distance between two consecutive compressions (or rarefactions). ### Properties - **Frequency** (measured in **Hertz, Hz**): Number of waves passing a point per second. **Higher frequency → higher pitch**. - **Amplitude**: Related to **volume** – larger amplitude means louder sound. ### Detection - **Microphone**: Converts sound wave into an electrical signal (vibrates a diaphragm). - **Oscilloscope**: Displays the electrical signal as a trace. - **Ear**: Sound vibrates the eardrum; vibrations become electrical signals sent to the brain. ### Key Facts - Human auditory range: **20 Hz – 20,000 Hz**. - **Ultrasound**: Frequency above 20,000 Hz. - Wavelength is NOT the distance between a compression and rarefaction (that's half a wavelength). - Frequency affects pitch, NOT loudness; amplitude affects loudness.

Sound wave: A longitudinal wave caused by a vibrating object, transferring energy through particle collisions.
Longitudinal wave: A wave where vibrations are parallel to the direction of wave travel.
Compression: Region in a sound wave where air particles are close together.
Rarefaction: Region in a sound wave where air particles are further apart.
Wavelength: The distance between one compression and the next (or one rarefaction and the next).
Frequency: A measure of how many sound waves pass a point every second, measured in Hertz (Hz). Higher frequency gives higher pitch.
Amplitude: The size of the vibration; larger amplitude means louder sound.
Microphone: A device that converts a sound wave into an electrical signal by vibrating a diaphragm.
Oscilloscope: A device that displays an electrical signal from a microphone as a trace on a screen.
Ultrasound: Sound waves with a frequency above 20,000 Hz.

字卡

What causes a sound wave?

An object that is vibrating makes a sound wave.

What type of wave is sound?

Sound is a longitudinal wave.

In a longitudinal wave, the vibrations are ________ to the direction of wave travel.

parallel

What are compressions in a sound wave?

Compressions are regions where air particles are close together.

What are rarefactions in a sound wave?

Rarefactions are regions where air particles are further apart.

What is the wavelength of a sound wave?

The distance between one compression and the next (or one rarefaction and the next).

What is frequency?

A measure of how many sound waves pass a point every second.

What unit is frequency measured in?

Hertz (Hz).

How is frequency related to pitch?

The higher the frequency, the higher the pitch.

If 200 sound waves pass a point every second, what is the frequency?

200 Hz.

What is the auditory range for humans?

Any frequency between 20 and 20,000 Hz.

What is ultrasound?

A sound wave with a frequency above 20,000 Hz.

How is amplitude related to volume?

The larger the amplitude, the louder the sound wave.

What device turns a sound wave into an electrical signal?

A microphone.

What part of a microphone vibrates due to sound waves?

A diaphragm.

What device can display the electrical signal from a microphone as a trace?

An oscilloscope.

How do our ears detect sound waves?

Sound waves vibrate our ear drum; vibrations are turned into electrical signals sent to the brain.

True or false: The wavelength is the distance between a compression and a rarefaction.

False.

True or false: The higher the frequency of a sound wave, the louder it is.

False.

True or false: The lower the amplitude of a sound wave, the quieter it is.

True.

True or false: A microphone is used to turn a sound wave into an electrical signal.

True.

How does a vibrating object create a sound wave in air?

The object vibrates air particles, which collide with other air particles and transfer energy.

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