📚 Sound | IGCSE AQA Science Revision | 声 | IGCSE AQA 科学考点精讲
In IGCSE AQA Science, the topic of sound bridges the physics of waves with our everyday experience. You will explore how sound travels as a longitudinal wave, why different instruments produce different notes, and how the speed of sound can be measured. This revision guide systematically covers all key AQA specification points – from frequency and pitch to echoes, ultrasound, and hearing – to help you master the topic for your examination.
在 IGCSE AQA 科学中，声音这一主题将波的物理学与我们的日常体验联系起来。你将探索声音如何以纵波的形式传播，为什么不同乐器会发出不同的音调，以及如何测量声速。本复习指南系统地涵盖了 AQA 考试大纲中的所有关键考点——从频率和音调到回声、超声波和听觉——帮助你掌握这一主题，从容应对考试。
1. What is Sound? | 什么是声音？
Sound is a form of energy produced by vibrating objects. These vibrations cause the surrounding medium (usually air) to oscillate, transferring energy without any net movement of matter. Sound requires a medium to travel; it cannot propagate through a vacuum because there are no particles to carry the vibrations. This is famously demonstrated by the bell jar experiment, where a ringing bell becomes inaudible as air is pumped out.
声音是由物体振动产生的一种能量形式。这些振动使周围的介质（通常是空气）发生振荡，传递能量而物质本身不发生净移动。声音的传播需要介质；它无法在真空中传播，因为那里没有粒子可以承载振动。经典的钟罩实验证明了这一点：随着空气被抽出，罩内的铃声会逐渐消失。
In everyday life, we can feel sound vibrations when we touch a loudspeaker or a tuning fork. The back-and-forth motion of the source creates compressions and rarefactions in the air, forming a sound wave. The source of sound could be vocal cords, guitar strings, or a drum skin, all of which vibrate when struck or excited.
在日常生活中，当我们触摸扬声器或音叉时，就能感受到声音的振动。声源的前后运动在空气中形成疏密相间的区域，构成了声波。声源可以是声带、吉他弦或鼓面，它们在受到敲击或激发时都会振动。
2. Sound as a Longitudinal Wave | 声波是纵波
Sound waves are longitudinal waves. This means the vibrations of the particles are parallel to the direction of wave travel. In a longitudinal wave, regions where particles are close together are called compressions, and regions where they are spread apart are called rarefactions. It is essential to contrast this with transverse waves (e.g. light, ripples on water), where particle oscillation is perpendicular to wave motion.
声波是纵波。这意味着粒子的振动方向与波的传播方向平行。在纵波中，粒子密集的区域称为压缩区，粒子稀疏的区域称为稀疏区。必须将纵波与横波（如光、水波）进行对比，横波中粒子的振动方向垂直于波的传播方向。
When drawing or interpreting diagrams of sound waves, you may represent compressions as lines closer together and rarefactions as lines farther apart. The wavelength is the distance between the centres of two successive compressions (or two successive rarefactions). Although sound is longitudinal, we often use a transverse displacement–distance graph to represent its pressure variations.
在绘制或解读声波图时，可以用较密的线条表示压缩区，较疏的线条表示稀疏区。波长是两个相邻压缩区（或稀疏区）中心之间的距离。虽然声波是纵波，但我们常使用横向的位移–距离图来表示其压强变化。
3. Wave Properties of Sound | 声波的波动性质
mplitude is the maximum displacement of particles from their resting position, which determines how much energy the wave carries.
和所有波一样，声波可以用振幅、波长、频率和速度来描述。频率（f）是每秒完整振动的次数，单位为赫兹（Hz）。周期（T）是一次完整振动所需的时间，二者满足 T = 1 ÷ f。振幅是粒子偏离平衡位置的最大位移，它决定了波携带的能量大小。
ese properties together. For sound in air at room temperature, the speed is approximately 340 m/s, but this value can vary with temperature and humidity. You should be prepared to calculate any of the three quantities when two are given, and to rearrange the equation confidently.
波速公式 v = f × λ 将这些性质联系在一起。室温下声音在空气中的传播速度约为 340 m/s，但这一数值会随温度和湿度变化。你需要能够根据已知的两个量计算第三个量，并熟练地变换公式。
v = f × λ
速度 = 频率 × 波长
4. Speed of Sound | 声音的速度
The speed of sound differs in solids, liquids, and gases. Sound travels fastest in solids because particles are closely packed and can quickly pass on vibrations. It travels slower in liquids and slowest in gases, where particles are further apart. For example, the speed of sound in steel is about 5000 m/s, in water about 1500 m/s, and in air roughly 340 m/s.
声音在固体、液体和气体中的传播速度不同。声在固体中传播最快，因为粒子紧密排列，能够迅速传递振动。它在液体中较慢，在气体中最慢，因为气体粒子间距较大。例如，钢铁中的声速约为 5000 m/s，水中约为 1500 m/s，空气中约为 340 m/s。
distance ÷ time. Remember the total distance travelled is twice the distance to the wall.
AQA 规定的一项实验是测量空气中的声速，方法可以是利用远处墙壁产生的回声，或通过拍手和回声计时。测量墙壁的距离以及回声返回所需的时间后，就可以用速度 = 距离 ÷ 时间计算声速。记住，声波往返的总距离是墙壁距离的两倍。
5. Frequency and Pitch | 频率与音调
Pitch is the human perception of how high or low a sound is, and it is directly related to the frequency of the sound wave. A high-frequency wave (e.g. 2000 Hz) produces a high-pitched sound, while a low-frequency wave (e.g. 100 Hz) produces a low-pitched sound. The typical range of human hearing is from about 20 Hz to 20 000 Hz, though this narrows with age.
音调是人类对声音高低的主观感受，它与声波的频率直接相关。高频波（例如 2000 Hz）会发出高音调的声音，而低频波（例如 100 Hz）会发出低音调的声音。人类听觉的典型范围约为 20 Hz 至 20 000 Hz，但这一范围会随着年龄增长而变窄。
On an oscilloscope screen, a higher frequency wave shows more cycles in the same time interval, meaning the waveform is more tightly packed. Doubling the frequency of a musical note raises its pitch by one octave. In music, different notes correspond to specific frequencies, which explains why a violin sounds much higher than a double bass.
在示波器屏幕上，高频波在相同时间间隔内显示出更多的周期，即波形更加密集。将一个音符的频率加倍，其音调会升高一个八度。在音乐中，不同的音符对应特定的频率，这解释了为什么小提琴的声音比低音提琴高得多。
6. Amplitude and Loudness | 振幅与响度
Loudness is the subjective measure of how quiet or loud a sound appears to our ears, and it is chiefly determined by the amplitude of the sound wave. A larger amplitude means the wave carries more energy, causing greater pressure variations and making the sound seem louder. Loudness is frequently measured in decibels (dB), a logarithmic scale where a 10 dB increase corresponds to a tenfold increase in sound intensity.
响度是声音在我们耳朵中显得安静或响亮的主观量度，它主要由声波的振幅决定。振幅越大，意味着波携带的能量越多，造成的压力变化越大，声音听起来就越响。响度通常用分贝（dB）来衡量，这是一个对数标度，每增加 10 dB 相当于声音强度增大十倍。
On an oscilloscope trace, loudness is shown by the height (amplitude) of the wave. A louder sound produces taller peaks, whereas a quieter sound produces shorter ones. It is important not to confuse loudness with pitch; a high-pitched sound can be quiet, and a low-pitched sound can be loud. The human ear is more sensitive to mid-range frequencies than to very low or very high ones.
在示波器轨迹上，响度由波的高度（振幅）显示。声音越响，峰值越高；声音越轻，峰值越低。切勿将响度与音调混淆；高音调的声音可能很轻，而低音调的声音可能很响。人耳对中频的敏感度高于低频和高频。
7. Echoes and Reflection | 回声与反射
An echo is a reflected sound wave that arrives at the listener's ear more than 0.1 s after the original sound, allowing the brain to perceive it as a distinct second sound. This 0.1 s threshold arises from the persistence of hearing. If the reflecting surface is less than about 17 m away, the sound returns too quickly and blends into the original, producing reverberation rather than a clear echo.
回声是指反射回来的声波在原始声音发出超过 0.1 秒后才到达听者耳中，使大脑能够将其感知为独立的第二个声音。这一 0.1 秒的阈值源于听觉暂留。如果反射面距离不足约 17 米，声音就会返回得太快，与原始声音混合，产生混响，而非清晰的回声。
Reflection of sound obeys the law of reflection: the angle of incidence equals the angle of reflection. This principle is used in applications like sonar, radar, and medical ultrasound imaging. Hard, flat surfaces such as cliffs and large buildings produce strong echoes, while soft, porous materials like foam and curtains tend to absorb sound, reducing echoes.
声音的反射遵循反射定律：入射角等于反射角。这一原理应用于声纳、雷达和医学超声成像等领域。坚硬的平整表面，如悬崖和大型建筑物，会产生强烈的回声；而泡沫、窗帘等柔软、多孔的材料容易吸音，从而减少回声。
8. Ultrasound | 超声波
Ultrasound is sound with frequencies above the upper limit of human hearing, typically above 20 000 Hz (20 kHz). Because of its high frequency, ultrasound has a very short wavelength and can be directed in narrow beams. It can penetrate materials and is partially reflected at boundaries between different media, making it invaluable for imaging and measurement.
超声波是频率超过人类听觉上限的声音，通常指高于 20 000 Hz（20 kHz）的声波。由于频率高，超声波的波长非常短，可以被定向成狭窄的波束。它能穿透材料，并在不同介质的边界处发生部分反射，因此在成像和测量中极具价值。
In medicine, ultrasound is used for prenatal scanning to produce images of a fetus without using harmful ionising radiation. Pulses of ultrasound are sent into the body, and the reflected echoes are used to build up a real-time image. Sonar also uses ultrasound to detect objects underwater, measure depths, and locate shoals of fish. Industrial applications include flaw detection in metals and cleaning delicate components.
在医学领域，超声波用于产前扫描，生成胎儿图像，无需使用有害的电离辐射。超声波脉冲被送入体内，利用反射的回声构建实时图像。声纳也利用超声波探测水下物体、测量水深以及定位鱼群。工业应用包括金属探伤和精密零件的清洗。
9. The Ear and Hearing | 耳朵与听觉
The human ear is an extraordinary organ that converts sound waves into electrical signals interpreted by the brain. Sound waves are funnelled by the outer ear (pinna) into the ear canal, causing the eardrum to vibrate. These vibrations are transferred through three tiny bones in the middle ear – the hammer, anvil, and stirrup – which amplify the vibrations and transmit them to the oval window of the cochlea in the inner ear.
人耳是一个非凡的器官，能将声波转化为大脑解读的电信号。声波经外耳（耳廓）收集进入耳道，引起鼓膜振动。这些振动通过中耳的三块小骨——锤骨、砧骨和镫骨——传递，它们将振动放大并传送至内耳耳蜗的卵圆窗。
Inside the fluid‑filled cochlea, hair cells convert the mechanical vibrations into nerve impulses that travel along the auditory nerve to the brain. Prolonged exposure to loud sounds can damage these hair cells, leading to permanent hearing loss. The safe listening time decreases as sound intensity rises; the AQA specification emphasises awareness of the dangers of noise pollution and hearing protection.
在充满液体的耳蜗内，毛细胞将机械振动转化为神经冲动，沿听神经传递至大脑。长时间暴露于响亮的噪声中会损伤这些毛细胞，导致永久性听力损失。安全的聆听时间随声音强度的增加而缩短；AQA 考试大纲强调对噪声污染危害的认知以及听力保护意识。
10. Sound Insulation and Absorption | 隔音与吸音
Reducing unwanted sound is an important engineering task. Sound absorption occurs when materials take in sound energy and dampen the vibrations, converting them into a tiny amount of heat. Soft, porous materials like carpets, foam, and fibreglass are good sound absorbers. Sound insulation, by contrast, aims to block the transmission of sound, often by using dense, massive barriers or creating a vacuum layer.
减少不必要的噪声是一项重要的工程任务。吸音是指材料吸收声能并抑制振动，将其转化为微量的热能。地毯、泡沫和玻璃纤维等柔软多孔的材料是良好的吸音体。相比之下，隔音旨在阻隔声音的传播，通常通过使用厚重密实的屏障或设置真空层来实现。
In the AQA syllabus, you may be asked to evaluate methods for reducing noise in a room or between rooms. Double‑glazed windows reduce external noise because the trapped air layer and additional glass pane disrupt the path of the sound wave. Recording studios often use anechoic chambers with foam wedges to minimise echoes and achieve near‑silent conditions.
在 AQA 课程中，你可能会被要求评估减少室内或房间之间噪声的方法。双层玻璃窗可以减少外部噪声，因为夹层中的空气和额外的玻璃板会阻断声波的传播路径。录音棚经常使用带有泡沫楔块的消声室，以最大程度减少回声并实现近乎无声的环境。
11. Using Sound Waves | 声音的应用
× t) ÷ 2, where v is the speed of sound in water and t is the time for the echo to return.
除超声波外，声波还有许多实际应用，这些在 IGCSE 科学中均有涉及。声纳（声音导航与测距）发射超声波脉冲并检测其回声，以确定水下距离。可以使用公式 深度 = (v × t) ÷ 2 计算海底深度，其中 v 为声在水中的速度，t 为回声返回的时间。
Seismic waves, which are a type of sound wave travelling through the Earth, help geophysicists map subsurface structures. Musical instruments exploit standing waves, where the length of an air column or string determines the pitch. In industry, ultrasonic cleaning uses high‑frequency vibrations to remove dirt from objects. All these examples underline that understanding sound is not just academic – it has real‑world impact.
地震波是一种在地球内部传播的声波，能帮助地球物理学家绘制地下结构图。乐器利用驻波原理，气柱或琴弦的长度决定了音高。在工业中，超声波清洗利用高频振动去除物体上的污垢。所有这些例子都说明，理解声音不仅是理论学习，更具有实际影响力。
12. Exam Tips and Common Mistakes | 考试技巧与常见错误
When answering AQA questions on sound, always state clearly that sound is a longitudinal wave and explain what that means – particle vibrations parallel to energy transfer. Avoid the common confusion between transverse and longitudinal graphs; just because a diagram looks like a transverse wave does not mean the actual wave is transverse. When describing echoes, link the 0.1 s persistence of hearing to the minimum distance for a clear echo and show your working clearly.
在回答 AQA 中关于声音的问题时，务必明确指出声波是纵波，并解释其含义——粒子的振动方向与能量传递方向平行。要避免常见的将横波图和纵波图混淆的错误；图示看起来像横波，并不代表实际波就是横波。在描述回声时，应将 0.1 秒的听觉暂留与产生清晰回声的最小距离联系起来，并清晰地展示计算步骤。
s. In calculations, remember that the distance travelled by a reflected pulse is twice the distance to the reflecting surface. When discussing pitch and loudness, always associate pitch with frequency and loudness with amplitude – mix‑ th standard and rearranged forms, and be ready to comment on how changes in one variable affect another.
单位使用要精确：频率用 Hz，时间用 s，距离用 m，速度用 m/s。在计算中，记住反射脉冲行进的距离是到反射面距离的两倍。在讨论音调和响度时，始终将音调关联频率、响度关联振幅——这两者一旦混淆就会丢分。最后，练习使用波方程 v = f × λ 的标准形式和变形，并准备好分析一个变量的变化如何影响其他变量。
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