IGCSE OCR Science: Sound – Complete Revision Guide | IGCSE OCR 科学：声

📚 IGCSE OCR Science: Sound – Complete Revision Guide | IGCSE OCR 科学：声 – 考点精讲

Sound is a key topic in the IGCSE OCR Science (Physics) syllabus. Understanding how sound waves are produced, how they travel, and how we perceive them is essential for tackling exam questions on wave properties. This revision guide covers every critical concept, from the basic definition of a sound wave to advanced applications of ultrasound, supported by clear diagrams, worked examples, and typical examination tips.

声音是 IGCSE OCR 科学（物理）大纲中的重要主题。理解声波如何产生、如何传播以及我们如何感知声音，对于解答波的性质相关考题至关重要。本复习指南涵盖了从声波基本定义到超声波高级应用的每一个关键概念，并配有清晰的图示、解析范例和典型的考试技巧。

1. What is Sound? | 什么是声音？

Sound is a form of energy produced by vibrating objects. These vibrations cause particles in a medium (solid, liquid or gas) to oscillate, creating a longitudinal wave. In a longitudinal wave, particles vibrate parallel to the direction of energy transfer. Sound cannot travel through a vacuum because there are no particles to carry the vibrations.

声音是由振动物体产生的一种能量形式。这些振动会使介质（固体、液体或气体）中的粒子发生振荡，从而形成纵波。在纵波中，粒子的振动方向与能量传递方向平行。声音不能在真空中传播，因为没有粒子来传递振动。

The key characteristic of a longitudinal sound wave is the series of compressions (regions of high pressure where particles are close together) and rarefactions (regions of low pressure where particles are spread apart). These alternating compressions and rarefactions travel through the medium, transferring sound energy from one place to another.

纵波声波的关键特征是一系列的压缩（粒子聚集的高压区域）和稀疏（粒子分散的低压区域）。这些交替的压缩和稀疏在介质中传播，将声音能量从一个地方传递到另一个地方。

2. Production of Sound | 声音的产生

Sound is produced whenever an object vibrates. For example, a tuning fork vibrating after being struck pushes air molecules together to form a compression, then moves back to form a rarefaction. Similarly, in a loudspeaker, a cone moves rapidly back and forth, driven by an alternating electrical signal, creating sound waves. Musical instruments rely on vibrating strings (guitar), air columns (flute), or membranes (drum).

每当物体振动时，就会产生声音。例如，被敲击后的音叉振动，将空气分子推到一起形成压缩，然后向后移动形成稀疏。同样，在扬声器中，音盆在交变电信号的驱动下快速前后移动，产生声波。乐器则依赖于振动的琴弦（吉他）、空气柱（长笛）或薄膜（鼓）发声。

The frequency of the vibration determines the pitch of the sound; the larger the amplitude of vibration, the louder the sound. In all cases, the vibrating source must be in contact with a medium to transmit the disturbance.

振动的频率决定了声音的音调；振动幅度越大，声音越响。在所有情况下，振动源必须与介质接触才能传递扰动。

3. Transmission of Sound Through Media | 声音通过介质的传播

Sound requires a material medium for transmission. It travels fastest in solids, slower in liquids, and slowest in gases. This is because particles in a solid are closely packed and can quickly pass on vibrations. In gases, particles are far apart, so the transfer of vibrational energy takes longer. For example, the speed of sound in air (at 20 °C) is about 343 m/s, in water about 1500 m/s, and in steel about 5000 m/s.

声音需要物质介质才能传播。它在固体中传播最快，在液体中较慢，在气体中最慢。这是因为固体中的粒子紧密排列，能快速传递振动。而在气体中，粒子相距较远，振动能量的传递需要更长时间。例如，声音在空气（20 °C）中的速度约为 343 m/s，在水中约为 1500 m/s，在钢中约为 5000 m/s。

Temperature also affects the speed of sound in air: higher temperatures increase the kinetic energy of particles, allowing them to collide more frequently and transmit the wave faster. The relationship between speed (v), frequency (f) and wavelength (λ) is given by the wave equation:

温度也会影响空气中声音的速度：温度越高，粒子的动能越大，使得它们碰撞更频繁，波传递得更快。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 applies to all waves, including sound.

该方程适用于包括声音在内的所有波。

4. Frequency and Pitch | 频率与音调

The frequency of a sound wave is the number of complete vibrations (or waves) passing a point per second, measured in hertz (Hz). Frequency determines the pitch of a sound: a high-frequency wave produces a high-pitched note, while a low-frequency wave produces a low-pitched note. A typical human ear can detect frequencies ranging from about 20 Hz to 20 000 Hz.

声波的频率是指每秒钟通过某一点的完整振动（或波）的次数，单位为赫兹 (Hz)。频率决定了声音的音调：高频波产生高音调的声音，低频波产生低音调的声音。正常人耳能探测到的频率范围约为 20 Hz 至 20 000 Hz。

On an oscilloscope display, a higher frequency appears as more wave cycles across the screen for the same time base setting. For a sound wave of fixed speed, doubling the frequency halves the wavelength. This inverse relationship is often tested in calculations.

在示波器显示上，对于相同的时基设置，频率越高，屏幕上显示的波形周期就越多。对于速度固定的声波，频率翻倍则波长减半。这种反比关系经常在计算题中出现。

5. Amplitude and Loudness | 振幅与响度

Amplitude is the maximum displacement of a particle from its rest position as a wave passes. The larger the amplitude, the more energy the wave carries, and therefore the louder the sound. Loudness is a subjective perception, but it correlates strongly with the physical amplitude of the sound wave. On an oscilloscope, a louder sound shows a taller wave (greater vertical displacement).

振幅是波通过时粒子偏离其平衡位置的最大位移。振幅越大，波携带的能量越多，因此声音越响。响度是一种主观感受，但它与声波的物理振幅密切相关。在示波器上，更响的声音显示为更高的波形（垂直位移更大）。

It is important not to confuse amplitude with frequency. A quiet, high-pitched sound can have a small amplitude but high frequency; a loud, low-pitched sound can have a large amplitude but low frequency. Both amplitude and frequency can be altered independently.

重要的是不要将振幅与频率混淆。一个轻柔的高音调声音可以具有小振幅却高频率；一个响亮的低音调声音可以具有大振幅却低频率。振幅和频率可以独立改变。

6. Waveform and Quality (Timbre) | 波形与音色（音质）

Pure sounds, such as those from a tuning fork, produce a smooth, regular waveform called a sine wave. Most sounds, however, are a mixture of many frequencies. The specific pattern of the waveform gives a sound its distinctive quality or timbre. This is why a violin and a flute playing the same note at the same loudness sound different – their waveforms are different, even if the fundamental frequency is the same.

纯音，例如音叉发出的声音，产生一种平滑、规则的波形，称为正弦波。然而，大多数声音是多种频率的混合。波形的特定模式赋予声音其独特的音质或音色。这就是为什么小提琴和长笛演奏相同音高和响度的音符时听起来不同——即使基频相同，它们的波形也不同。

An oscilloscope can display these complex waveforms. Musical instruments produce rich waveforms containing the fundamental frequency plus higher harmonics. Noise, on the other hand, produces an irregular, jagged waveform without a clear repeating pattern.

示波器可以显示这些复杂的波形。乐器产生的丰富波形包含基频加上更高的泛音。另一方面，噪音产生的是不规则的锯齿状波形，没有清晰的重复模式。

7. Echo and Reflection of Sound | 回声与声音的反射

When sound waves strike a hard, flat surface, they are reflected. This reflection is called an echo. For a distinct echo to be heard, the reflecting surface must be at least 17 metres away from the source (assuming air at room temperature), because the brain needs about 0.1 seconds to distinguish between the original sound and the reflected sound.

当声波撞击坚硬的平坦表面时，它们会被反射。这种反射被称为回声。要听到清晰的回声，反射面必须距离声源至少 17 米（假设室温下的空气），因为大脑需要大约 0.1 秒来区分原声和反射声。

Echoes can be used to determine distances, for example in sonar systems or bat echolocation. The total distance travelled by the sound wave is speed × time. Since the sound travels to the surface and back, the distance to the object is half the calculated total distance:

回声可用于确定距离，例如在声纳系统或蝙蝠回声定位中。声波传播的总距离 = 速度 × 时间。由于声音传播到表面再返回，因此到物体的距离是计算出的总距离的一半：

d = (v × t) / 2

Multiple reflections can cause reverberation, which is the persistence of sound in a large hall. Soft furnishings absorb sound and reduce echoes.

多次反射会引起混响，即声音在大厅内持续的现象。柔软的家具可以吸收声音，减少回声。

8. Ultrasound and Its Uses | 超声波及其应用

Ultrasound refers to sound waves with frequencies above the upper limit of human hearing, i.e. greater than 20 000 Hz. Because of its high frequency and short wavelength, ultrasound can be produced in narrow beams and can penetrate materials. This makes it invaluable for various applications.

超声波是指频率高于人类听觉上限的声波，即大于 20 000 Hz。由于其高频和短波长，超声波可以形成窄波束并穿透材料。这使得它在各种应用中极具价值。

Medical imaging: Ultrasound scans (sonography) are used to view internal body structures, such as a fetus during pregnancy. The waves are reflected at boundaries between different tissues, and the reflection times are used to build an image.
医学成像：超声波扫描用于观察内部身体结构，例如孕期胎儿。波在不同组织的边界处反射，反射时间用于构建图像。
Industrial testing: Ultrasound is used to detect flaws or cracks in metals and pipelines. A change in the reflection pattern indicates a defect.
工业检测：超声波用于检测金属和管道中的缺陷或裂纹。反射模式的变化表明存在缺陷。
SONAR: Ships use ultrasound for depth sounding and detecting objects underwater; bats use it for navigation.
声纳：船舶使用超声波进行深度探测和探测水下物体；蝙蝠使用超声波进行导航。

Ultrasound is non-ionising and considered safer than X-rays for many diagnostic purposes.

超声波是非电离的，在许多诊断用途中被认为比 X 射线更安全。

9. The Human Ear and Hearing Range | 人耳与听觉范围

The human ear converts sound waves into electrical signals that the brain interprets. Sound enters the ear canal, causing the eardrum to vibrate. These vibrations are passed through tiny bones (ossicles) in the middle ear to the cochlea in the inner ear. The cochlea contains hair cells that transform vibrations into nerve impulses sent to the brain via the auditory nerve.

人耳将声波转换为大脑能够解读的电信号。声音进入耳道，引起鼓膜振动。这些振动通过中耳的小骨（听小骨）传递到内耳的耳蜗。耳蜗内有毛细胞，能将振动转化为神经冲动，通过听觉神经传送到大脑。

Young people can typically hear frequencies from 20 Hz to 20 000 Hz, but the upper limit decreases with age. Exposure to very loud sounds can permanently damage hair cells, leading to hearing loss. Using ear protection and keeping volume at safe levels can prevent damage.

年轻人通常能听到 20 Hz 到 20 000 Hz 的频率，但上限会随年龄增长而降低。暴露在非常大的声音中会永久性损伤毛细胞，导致听力损失。使用听力保护装置并将音量保持在安全水平可以防止损伤。

10. The Speed of Sound Experiment | 声速测量实验

A common method to measure the speed of sound in air uses a pair of microphones connected to an oscilloscope or data logger, placed a known distance apart. A sharp sound (e.g. from two wooden blocks struck together) is made near one microphone. The time delay between the two traces on the oscilloscope is measured. Speed is calculated as distance between microphones divided by time delay.

一种常见的测量空气中声速的方法使用一对连接到示波器或数据记录器的麦克风，它们相距已知距离。在其中一个麦克风附近制造一个尖锐的声音（例如两块木块敲击）。测量示波器上两道光迹之间的时间延迟。速度 = 麦克风间距 / 时间延迟。

Alternatively, an echo method can be used: standing a known distance from a large wall, clapping and adjusting the rhythm until each clap coincides with the previous echo. The time for a known number of claps gives the time for a round trip, from which speed can be calculated.

或者，可以使用回声法：站在离一堵大墙已知距离的地方，拍手并调整节奏，直到每次拍手与前一次回声重合。已知次数的拍手时间给出了往返时间，由此可算出速度。

11. Interpreting Oscilloscope Traces | 示波器波形分析

In the exam, you are often asked to interpret oscilloscope diagrams showing sound waves. Remember the key controls: the y-gain (volts/div) sets the scale for amplitude, and the time base (seconds/div) sets the horizontal scale. To find the period (T), count the number of divisions for one complete cycle and multiply by the time base setting. Frequency is the reciprocal of period: f = 1/T. Amplitude is the peak voltage reading, which can be compared directly for loudness.

考试中，常常要求解释显示声波的示波器图形。记住关键的控制旋钮：y 增益（伏特/格）设置振幅的比例尺，时基（秒/格）设置水平比例尺。要找到周期 (T)，计算一个完整周期的格数，再乘以时基设置。频率是周期的倒数：f = 1/T。振幅是峰值电压读数，可直接比较响度。

Be careful: if the time base is switched off, the trace appears as a vertical line whose height indicates amplitude but cannot show frequency. With time base on, the waveform spreads horizontally.

注意：如果时基关闭，波形显示为一条垂直线，其高度表示振幅，但无法显示频率。当时基打开时，波形沿水平方向展开。

12. Summary and Exam Tips | 总结与考试技巧

Revise these core points: sound is a longitudinal wave; it requires a medium; speed equation v = fλ; amplitude relates to loudness, frequency to pitch; reflection produces echoes; ultrasound applications; and oscilloscope interpretation. Be ready to apply the wave equation in calculations, paying attention to unit conversions (e.g., ms to s, cm to m). Always explain physical concepts using particle vibrations and energy transfer.

复习这些核心要点：声音是纵波；它需要介质；波速公式 v = fλ；振幅与响度相关，频率与音调相关；反射产生回声；超声波应用；以及示波器解读。准备好应用波动方程进行计算，注意单位转换（例如，毫秒转为秒，厘米转为米）。始终使用粒子振动和能量传递来解释物理概念。

When describing sound transmission, mention the series of compressions and rarefactions. For echo questions, remember the factor of 2 for round-trip distance. Finally, be able to sketch waveforms to show differences in pitch and loudness, labeling axes clearly.

在描述声音传播时，要提及连续的压缩和稀疏。对于回声问题，记住往返距离的因子 2。最后，要能够绘制波形图来显示音调和响度的差异，并清晰地标注坐标轴。

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IGCSE OCR Science: Sound – Complete Revision Guide | IGCSE OCR 科学：声 – 考点精讲