📚 Sound IGCSE Science Revision | IGCSE 科学：声 考点精讲
Sound is a form of energy produced by vibrating objects. It travels through solids, liquids and gases as a longitudinal wave, but cannot travel through a vacuum. In IGCSE Science, understanding the properties, behaviour and applications of sound waves is essential for mastering the waves topic. This revision guide covers everything from wave equations to ultrasound, with clear explanations and exam-focused pointers.
声音是由物体振动产生的一种能量形式。它以纵波的形式在固体、液体和气体中传播，但无法在真空中传播。在 IGCSE 科学课程中，掌握声波的特性、行为和应用对于学好波动这一主题至关重要。本考点精讲涵盖从波动方程到超声波的所有内容，配有清晰的解释和紧扣考试的要点。
1. What is Sound? | 什么是声音？
Sound is a mechanical wave that transfers energy through a medium by causing particles to vibrate back and forth. It requires a material medium — solid, liquid or gas — to travel; it cannot propagate in a vacuum because there are no particles to carry the vibrations. The source of any sound is always a vibrating object, such as a guitar string, a drum skin or human vocal cords.
声音是一种机械波，它通过使介质粒子来回振动来传递能量。声音需要物质介质——固体、液体或气体——才能传播；它无法在真空中传播，因为没有粒子来传递振动。任何声音的源头始终是振动的物体，比如吉他弦、鼓面或人的声带。
2. Sound as a Longitudinal Wave | 声是纵波
Sound waves are longitudinal, meaning the vibrations of particles are parallel to the direction of energy transfer. As a sound wave travels, it creates regions of high pressure called compressions and regions of low pressure called rarefactions. These alternating compressions and rarefactions move through the medium, carrying energy without moving the particles permanently from their positions.
声波是纵波，这意味着粒子的振动方向与能量传递方向平行。当声波传播时，它会形成高压区域（称为密部）和低压区域（称为疏部）。这些交替的密部和疏部在介质中移动，携带能量，而不会使粒子永久离开其位置。
3. Describing Sound Waves | 描述声波
Like all waves, sound waves can be described by frequency, wavelength, amplitude and speed. Frequency (f), measured in hertz (Hz), is the number of complete vibrations per second; it determines the pitch. Wavelength (λ) is the distance between two consecutive compressions. Amplitude is the maximum displacement of particles from their rest position and relates to loudness. Wave speed (v) is how fast the wave travels through the medium.
像所有波一样，声波可以用频率、波长、振幅和速度来描述。频率（f），以赫兹（Hz）为单位，是每秒完整振动的次数；它决定音调。波长（λ）是两个相邻密部之间的距离。振幅是粒子离开其平衡位置的最大位移，与响度有关。波速（v）是声波在介质中传播的快慢。
4. Speed of Sound in Different Media | 声在不同介质中的速度
Sound travels at different speeds depending on the medium. In general, sound travels fastest in solids, slower in liquids and slowest in gases. This is because particles are closer together in solids, allowing vibrations to be passed on more quickly. The table below shows typical speeds:
声音在不同介质中的传播速度不同。一般来说，声在固体中最快，液体中较慢，气体中最慢。这是因为固体中粒子排列更紧密，振动能更快地传递。下表显示了典型速度：
| Medium 介质 | Speed of Sound (m/s) 声速（米/秒） |
|---|---|
| Air (20°C) | 343 |
| Water | 1500 |
| Steel | ~5000 |
Note that temperature also affects the speed in gases: higher temperature increases the speed of sound in air.
注意，温度也会影响气体中的声速：温度升高，空气中的声速也会增加。
5. The Wave Equation for Sound | 声波的波动方程
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
This equation is essential for solving IGCSE questions. For example, if a sound wave has a frequency of 500 Hz and a wavelength of 0.68 m, its speed is v = 500 × 0.68 = 340 m/s. Remember to use consistent units: speed in m/s, frequency in Hz, wavelength in metres.
该方程对于解答 IGCSE 试题至关重要。例如，如果一个声波的频率为 500 Hz，波长为 0.68 m，则其速度为 v = 500 × 0.68 = 340 m/s。记得使用一致的单位：速度用 m/s，频率用 Hz，波长用米。
6. Echoes and Reflection | 回声与反射
When sound waves strike a hard, flat surface, they can be reflected, producing an echo. An echo is a distinct, delayed repetition of the original sound. To calculate the distance to a reflecting surface, use the formula: distance = (speed of sound × time) / 2. The division by 2 accounts for the round trip of the sound wave. A common IGCSE problem involves timing an echo to measure distance.
当声波碰到坚硬、平坦的表面时，会被反射，产生回声。回声是原始声音的一个清晰、延迟的重复。计算到反射面的距离，使用公式：距离 = （声速 × 时间）/ 2。除以 2 是因为声波走了往返路程。IGCSE 常见的问题涉及利用回声计时来测量距离。
7. Ultrasound | 超声波
Ultrasound refers to sound waves with frequencies higher than 20 000 Hz (20 kHz), which is above the upper limit of human hearing. Ultrasound has many applications: in medicine for prenatal scanning and breaking up kidney stones; in industry for cleaning delicate equipment and detecting flaws in materials (non-destructive testing); and in sonar for measuring ocean depth or locating fish shoals. Ultrasound travels in a narrow beam and reflects at boundaries, making it ideal for imaging.
超声波指频率高于 20 000 Hz（20 kHz）的声波，超出了人耳听觉的上限。超声波有许多应用：医学中用于产前扫描和粉碎肾结石；工业中用于清洗精密仪器和检测材料缺陷（无损检测）；声呐中用于测量海洋深度或探测鱼群。超声波以窄束传播并在边界反射，非常适合成像。
8. Pitch and Loudness | 音调与响度
Pitch is determined by the frequency of a sound wave: a high-frequency wave produces a high-pitched sound, while a low-frequency wave produces a low-pitched sound. Loudness is determined by the amplitude: a larger amplitude means a louder sound. In an oscilloscope trace, frequency is shown by the number of waves across the screen, and amplitude by the height of the waves. Quality or timbre allows us to distinguish between different sources playing the same pitch and loudness.
音调由声波的频率决定：高频波产生高音调的声音，低频波产生低音调的声音。响度由振幅决定：振幅越大，声音越响。在示波器轨迹上，频率表现为屏幕上振动的次数，振幅表现为波形的高度。音色（音质）使我们能够区分发出相同音调和响度的不同声源。
9. The Human Ear and Hearing Range | 人耳与听觉范围
The human ear can detect sounds in the frequency range of approximately 20 Hz to 20 000 Hz. Sounds below 20 Hz are called infrasound, and those above 20 kHz are ultrasound. The ear converts sound vibrations into electrical signals in three main steps: the outer ear funnels sound to the eardrum, the middle ear bones amplify the vibrations, and the inner ear’s cochlea converts them into nerve impulses. Hearing range decreases with age, especially at high frequencies.
人耳能探测到的声音频率范围大约是 20 Hz 到 20 000 Hz。低于 20 Hz 的声音称为次声，高于 20 kHz 的称为超声波。耳朵通过三个主要步骤将声振动转化为电信号：外耳将声音引导到鼓膜，中耳听小骨放大振动，内耳的耳蜗将其转化为神经冲动。听觉范围随年龄增长而下降，尤其是高频部分。
10. Sound Waves on an Oscilloscope | 示波器上的声波
An oscilloscope connected to a microphone can display sound waves as transverse waveforms for easy analysis. A pure musical note gives a smooth, regular sine wave. A louder sound has taller peaks (greater amplitude); a higher-pitched sound has more cycles across the screen (higher frequency). Noise or complex sounds produce irregular, jagged traces. Comparing these traces is a classic IGCSE skill.
示波器连接麦克风可以将声波显示为横波波形，便于分析。纯乐音给出平滑、规则的正弦波。更响的声音具有更高的波峰（振幅更大）；更高音调的声音在屏幕上有更多的周期（频率更高）。噪声或复杂声音产生不规则、锯齿状的轨迹。比较这些轨迹是 IGCSE 的经典技能。
11. Diffraction of Sound | 声的衍射
Sound waves can spread out after passing through a gap or around an obstacle; this is diffraction. The amount of diffraction is most noticeable when the wavelength is similar in size to the gap or obstacle. Because sound waves in air have wavelengths ranging from a few centimetres to several metres, they diffract significantly around everyday objects and through doorways. This is why you can hear someone speaking even when you cannot see them.
声波在经过缝隙或遇到障碍物后会扩展散开；这就是衍射。当波长与缝隙或障碍物的大小相近时，衍射现象最为明显。由于空气中的声波波长从几厘米到几米不等，它们能够在日常物体周围和门缝中明显衍射。这就是即使你看不到说话的人也能听到他们声音的原因。
12. Applications and Safety | 应用与安全
Sound has numerous applications: medical ultrasound, sonar, musical instruments, public address systems and hearing aids. However, prolonged exposure to loud sounds (above 85 dB) can damage hearing permanently. Excessive noise is a form of pollution that can cause stress and health problems. In industry, ear protection is mandatory in noisy environments, and sound insulation is used in buildings to reduce unwanted noise.
声音有许多应用：医用超声波、声呐、乐器、公共广播系统和助听器。然而，长期暴露在大声环境中（超过 85 分贝）会对听力造成永久性损伤。过度的噪音是一种污染，可能导致压力和健康问题。在工业中，嘈杂环境强制要求佩戴听力保护装置，建筑中则使用隔音材料来减少不必要的噪音。
Published by TutorHao | IGCSE Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导