📚 Sound Revision for IGCSE CIE Science | IGCSE CIE 科学：声 考点精讲
Sound is a form of energy that travels through matter as longitudinal waves. In the IGCSE CIE Science syllabus, understanding sound involves its production, propagation, characteristics, and practical applications. Key topics include the relationship between particle vibration and wave motion, the factors affecting the speed of sound, and how frequency and amplitude influence pitch and loudness. This guide consolidates all essential concepts you need for the exam.
声是一种通过物质以纵波形式传播的能量。在IGCSE CIE科学课程中，理解声音包括其产生、传播、特性及实际应用。核心考点涵盖质点振动与波动的关系、影响声速的因素，以及频率和振幅如何决定音调和响度。本指南汇总了考试所需的所有关键概念。
1. What is Sound? | 什么是声音？
Sound is a mechanical wave, meaning it requires a medium (solid, liquid, or gas) to travel. It cannot pass through a vacuum.
声音是一种机械波，这意味着它需要介质（固体、液体或气体）才能传播，无法在真空中传递。
Sound waves are longitudinal. In a longitudinal wave, the particles of the medium vibrate parallel to the direction of energy transfer, forming compressions and rarefactions.
声波是纵波。在纵波中，介质质点沿能量传递方向平行振动，形成压缩区与稀疏区。
A compression is a region where particles are close together, while a rarefaction is a region where particles are spread apart.
压缩区是质点聚集的区域，稀疏区是质点分散的区域。
The transfer of sound involves energy moving through the medium, but the medium itself does not travel from source to receiver; only the disturbance propagates.
声音的传递涉及能量在介质中移动，但介质本身并不从声源移动到接收者；只有扰动向前传播。
2. Production of Sound | 声音的产生
Sound is produced by vibrating objects. When an object vibrates, it causes the surrounding air (or other medium) to vibrate, generating a sound wave.
声音由振动物体产生。当一个物体振动时，它会带动周围的空气（或其他介质）振动，从而产生声波。
Examples include the strings of a guitar, the vocal cords in our throat, and the diaphragm of a loudspeaker. In each case, a back-and-forth motion sets the medium into oscillation.
例子包括吉他的琴弦、我们喉咙中的声带以及扬声器的振膜。在每种情况下，往复的运动都会使介质振荡。
The frequency of the sound wave matches the frequency of the vibrating source. If a tuning fork vibrates at 440 Hz, the resulting sound wave in air also has a frequency of 440 Hz.
声波的频率与振动源的频率一致。如果一支音叉以440 Hz振动，空气中产生的声波频率也是440 Hz。
In experiments, a signal generator can drive a loudspeaker to produce sound of a chosen frequency, helping to demonstrate the link between vibration rate and pitch.
在实验中，信号发生器可以驱动扬声器发出选定频率的声音，这有助于展示振动速率与音调之间的联系。
3. Transmission of Sound | 声音的传播
Sound travels fastest in solids, slower in liquids, and slowest in gases. This is because particles in solids are closer together, allowing vibrations to be passed on more quickly.
声音在固体中传播最快，在液体中较慢，在气体中最慢。这是因为固体中粒子间距更小，振动能更快地传递。
The medium must have elasticity and inertia for sound to propagate. Stiff, dense materials typically transmit sound at higher speeds.
介质必须具有弹性和惯性，声音才能传播。坚硬、致密的材料通常以更快的速度传递声音。
A vacuum cannot support sound transmission because there are no particles to vibrate. This is why an alarm bell ringing in a vacuum jar cannot be heard once the air is removed.
真空不能传播声音，因为没有粒子可以振动。这就是为什么真空罐中的闹钟在抽走空气后无法被听到的原因。
Typical values for the speed of sound are around 340 m/s in air, 1500 m/s in water, and 5000 m/s in steel.
典型的声速值在空气中约为340 m/s，在水中约为1500 m/s，在钢中约为5000 m/s。
| Medium | Speed of Sound (m/s) |
|---|---|
| Air (20 °C) | 343 |
| Water | 1482 |
| Steel | 5960 |
上表显示了不同介质中的声速。
4. Speed of Sound | 声速
The speed of sound in air is affected by temperature, humidity, and pressure (though to a lesser extent). It increases with rising temperature because warmer air particles move faster, aiding propagation.
空气中的声速受温度、湿度和气压（影响较小）的影响。声速随温度升高而增加，因为较暖的空气粒子运动更快，有助于传播。
The relationship between speed (v), frequency (f), and wavelength (λ) is given by the wave equation:
速度（v）、频率（f）和波长（λ）之间的关系由波动方程给出：
v = f × λ
where v is in metres per second (m/s), f in hertz (Hz), and λ in metres (m). This equation applies to all waves, including sound.
其中 v 的单位是米/秒 (m/s)，f 的单位是赫兹 (Hz)，λ 的单位是米 (m)。该方程适用于所有波，包括声波。
To measure the speed of sound in air, a common experiment uses two microphones connected to an oscilloscope. By placing them a known distance apart and measuring the time delay of a clap or pulse, you can calculate v = distance / time.
测量空气中声速的常见实验是使用两个连接示波器的麦克风。将它们相隔已知距离放置，并测量拍手或脉冲的时间延迟，即可计算 v = 距离 / 时间。
Alternatively, by altering the frequency and measuring the wavelength of a standing sound wave in a resonance tube, students can use v = fλ to determine the speed.
另一种方法是，通过改变频率并测量共振管中驻波的波长，学生可以使用 v = fλ 来确定声速。
5. Frequency and Pitch | 频率与音调
Frequency is the number of complete vibrations or waves passing a point per second, measured in hertz (Hz).
频率是每秒经过某点的完整振动或波的数量，单位为赫兹 (Hz)。
The pitch of a sound is determined by its frequency. A higher frequency produces a higher-pitched sound; a lower frequency gives a lower pitch.
声音的音调由其频率决定。频率越高，音调越高；频率越低，音调越低。
The human ear can detect frequencies ranging approximately from 20 Hz to 20 000 Hz (20 kHz). Frequencies below 20 Hz are called infrasound, and those above 20 kHz are called ultrasound.
人耳可察觉的频率范围大约为20 Hz 至 20 000 Hz (20 kHz)。低于20 Hz 的频率称为次声波，高于20 kHz 的称为超声波。
On an oscilloscope trace, a higher-frequency wave appears with more cycles across the horizontal axis in the same time period; visual comparison of pitch is thus possible.
在示波器轨迹上，高频波在相同的时间段内水平轴上有更多的周期；因此可以通过视觉比较音调。
6. Amplitude and Loudness | 振幅与响度
Amplitude is the maximum displacement of a particle from its rest position. In a sound wave, larger amplitude means the compressions are more compressed and the rarefactions more spread out.
振幅是质点离其平衡位置的最大位移。在声波中，振幅越大，意味着压缩区更加紧密，稀疏区更加稀疏。
Loudness is a subjective perception, but it is related to the amplitude of the wave. A larger amplitude results in a louder sound, while a smaller amplitude yields a softer sound.
响度是一种主观感受，但与波的振幅相关。振幅越大，声音越响亮；振幅越小，声音越柔和。
On an oscilloscope, the amplitude corresponds to the height of the wave trace from the centre line. The unit of amplitude for sound can be expressed as pressure variation, but for IGCSE you relate amplitude to loudness qualitatively.
在示波器上，振幅对应于波形轨迹到中心线的垂直高度。声音振幅的单位可以表示为压力变化，但在IGCSE中，你只需定性地将振幅与响度关联。
The energy transported by a sound wave is proportional to the square of its amplitude. Doubling the amplitude increases the energy carried by a factor of four.
声波传递的能量与振幅的平方成正比。振幅加倍，携带的能量增加三倍（即变为四倍）。
7. Waveform and Quality | 波形与音色
Quality (or timbre) is the characteristic that allows us to distinguish between two sounds of the same pitch and loudness, such as a violin and a piano playing the same note.
音色（或音品）是使我们能够区分具有相同音调和响度的两个声音的特性，比如小提琴和钢琴演奏同一个音符。
The quality of a sound depends on the waveform, which is the shape of the wave. Different instruments produce different overtones (harmonics), creating distinct wave patterns.
声音的音色取决于波形，即波的形状。不同的乐器产生不同的泛音（谐波），形成独特的波形图。
A pure tone is a sound of a single frequency, represented by a smooth sine wave on an oscilloscope. Most musical notes are complex waves formed by a fundamental frequency plus harmonics.
纯音是单一频率的声音，在示波器上表现为光滑的正弦波。大多数乐音是由基频加上谐波构成的复合波。
In the exam, you may be asked to identify which oscilloscope trace represents a louder sound (higher amplitude) or a higher pitch (shorter wavelength/more cycles), or which comes from a different instrument (different shape).
在考试中，你可能会被要求判断哪个示波器轨迹表示更响的声音（振幅更大）或更高的音调（波长更短/周期更多），或者哪个轨迹来自不同的乐器（形状不同）。
8. Echo and Ultrasound | 回声与超声波
An echo is a reflection of sound. Sound waves bounce off a hard, smooth surface and return to the listener after a noticeable time delay.
回声是声音的反射。声波从坚硬光滑的表面反弹回来，经过明显的时间延迟后回到听者耳中。
The minimum distance for a distinct echo in air is about 17 metres from the reflecting surface, assuming the speed of sound is 340 m/s and the human ear can distinguish a 0.1 s gap between the original and reflected sound.
在空气中，产生清晰回声的最小距离约为离反射面17米，这是假设声速为340 m/s 且人耳可分辨原声与反射声之间0.1秒的间隔。
Ultrasound is sound with frequencies above 20 000 Hz. It is used in sonar to determine the depth of the sea or to detect fish. A pulse of ultrasound is sent out, and the time for the echo to return is measured to calculate distance using the formula 2d = v × t.
超声波是频率高于20 000 Hz 的声音。它被用于声呐以测量海深或探测鱼群。发射一个超声波脉冲，并测量回声返回的时间，然后使用公式 2d = v × t 计算距离。
Ultrasound is also widely used in medical imaging (prenatal scanning) and in industrial cleaning because the high-frequency vibrations can remove dirt without damaging surfaces.
超声波也广泛用于医学成像（产前检查）和工业清洁，因为高频振动可以去除污垢而不损坏表面。
9. Human Hearing | 人类听觉
The human ear converts sound waves into electrical signals that the brain interprets. The outer ear collects sound and funnels it through the ear canal to the eardrum, which vibrates.
人耳将声波转换成大脑解读的电信号。外耳收集声音并将其通过耳道传向鼓膜，鼓膜随之振动。
These vibrations are transmitted via tiny bones (ossicles) in the middle ear to the cochlea in the inner ear, where hair cells transform mechanical movement into nerve impulses.
这些振动通过中耳内的小骨（听小骨）传递到内耳的耳蜗，耳蜗中的毛细胞将机械运动转化为神经冲动。
Hearing range varies between individuals and declines with age, especially the ability to hear high frequencies. Prolonged exposure to loud sounds can damage the hair cells permanently, leading to hearing loss.
听力范围因人而异，并随年龄增长而下降，尤其是高频听力。长时间暴露在嘈杂声音中可能永久损伤毛细胞，导致听力损失。
Sound level is measured in decibels (dB). A typical conversation is about 60 dB; prolonged noise above 85 dB can cause hearing damage. The threshold of pain is around 120 dB.
声级以分贝 (dB) 为单位。典型的谈话声约为60 dB；长时间处于85 dB 以上的噪声中可能造成听力损伤。疼痛阈约在120 dB。
10. Sound Level and Decibel Scale | 声级与分贝标度
The decibel (dB) is a logarithmic unit used to express the intensity of sound. An increase of 10 dB represents a tenfold increase in sound intensity.
分贝 (dB) 是用于表示声音强度的对数单位。增加10 dB 代表声音强度增大为原来的10倍。
Because the scale is logarithmic, a normal conversation (60 dB) is 1000 times more intense than a whisper (30 dB), even though the decibel difference is 30.
由于该标度是对数性质，正常谈话声 (60 dB) 的强度是轻声耳语 (30 dB) 的1000倍，尽管分贝差仅为30。
Extended exposure to high sound levels, for example in factories or nightclubs, can cause noise-induced hearing loss. Ear protection is advised when levels exceed 85 dB constantly.
长时间暴露在高声级环境中，例如工厂或夜总会，可能导致噪声性听力损失。当声级持续超过85 dB 时，建议使用护耳器具。
In the IGCSE syllabus, you need to be aware that sound can cause damage to the ear and that the decibel scale is used to quantify sound level.
在IGCSE大纲中，你需要知道声音可能对耳朵造成损伤，并且使用分贝标度来量化声级。
11. Applications of Sound | 声音的应用
Beyond hearing, sound has many practical applications. Ultrasound scanning in medicine uses high-frequency pulses to create images of internal body structures, especially during pregnancy.
除了听觉，声音还有许多实际应用。医学中的超声波扫描使用高频脉冲来生成身体内部结构的图像，特别是在孕期检查中。
SONAR (Sound Navigation and Ranging) exploits echo location with sound waves to map the seabed, locate submarines, or shoals of fish. The time delay of the echo allows distance calculation.
声呐（声音导航与测距）利用声波的回声定位来绘制海床地图、定位潜艇或鱼群。回声的时间延迟可用于距离计算。
In industry, high-intensity ultrasound is used for cleaning delicate items like jewelry, lenses, and surgical instruments. The cavitation effect dislodges dirt at microscopic levels.
在工业中，高强度超声波用于清洁精密物品，如珠宝、透镜和手术器械。空化效应在微观层面去除污垢。
Sound is also essential in music, communication, and warning systems. Loudspeakers convert electrical signals into sound waves, mimicking original vibrations accurately.
声音在音乐、通信和警报系统中也是必不可少的。扬声器将电信号转换成声波，准确地重现原始振动。
12. Key Formula and Summary | 关键公式与总结
The core wave equation v = fλ connects speed, frequency, and wavelength for sound. Master rearrangements: f = v / λ, λ = v / f.
核心波动方程 v = fλ 将声速、频率和波长联系起来。需熟练掌握变形：f = v / λ，λ = v / f。
Remember that loudness depends on amplitude, pitch depends on frequency, and timbre depends on waveform.
牢记响度取决于振幅，音调取决于频率，音色取决于波形。
Sound is a longitudinal mechanical wave requiring a medium; it cannot travel through a vacuum. The speed is greatest in solids, then liquids, then gases.
声音是一种需要介质的纵波机械波；它不能在真空中传播。速度在固体中最快，其次是液体，再次是气体。
Echoes and ultrasound are reflection-based phenomena with immense practical use, from measuring distances to medical imaging.
回声和超声波是基于反射的现象，具有巨大的实际用途，从测量距离到医学成像。
Understand the decibel scale as a measure of sound intensity and the risk of hearing damage from prolonged loud sound.
理解分贝标度作为声音强度的量度以及长期暴露在嘈杂声音中导致听力损伤的风险。
Revising these key points will equip you to tackle any sound-related question on the IGCSE CIE Science paper with confidence.
复习这些关键点将使你有信心应对IGCSE CIE科学试卷中任何与声音相关的问题。
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