📚 GCSE AQA Science: Sound Key Points | GCSE AQA 科学：声 考点精讲
Sound is a form of energy that travels as longitudinal waves through a medium such as air, water, or solids. In GCSE AQA Science, you need to understand how sound is produced, how it travels, its key wave properties, and applications such as ultrasound. This revision guide covers all the essential points in a clear, bilingual format to help you master the topic.
声音是一种能量形式，以纵波的形式在空气、水或固体等介质中传播。在 GCSE AQA 科学课程中，你需要理解声音如何产生、如何传播、其关键的波动特性以及超声波等应用。本复习指南以清晰的双语形式涵盖所有要点，帮助你掌握这一主题。
1. What is Sound? | 什么是声音？
Sound is a type of mechanical wave caused by vibrations. It requires a medium to travel and cannot propagate through a vacuum. The vibrations cause particles in the medium to oscillate back and forth parallel to the direction of energy transfer, making sound a longitudinal wave.
声音是由振动引起的一种机械波。它需要介质才能传播，不能在真空中传播。振动使介质中的粒子沿着能量传递方向前后振荡，因此声音是一种纵波。
In a longitudinal wave, compressions are regions where particles are close together, and rarefactions are regions where particles are spread apart. Sound waves consist of alternating compressions and rarefactions.
在纵波中，密部是粒子聚集在一起的区域，疏部是粒子分散的区域。声波由交替的密部和疏部组成。
2. Production and Transmission of Sound | 声音的产生与传播
Sound is produced when an object vibrates, such as a loudspeaker cone, a guitar string, or vocal cords. These vibrations disturb the surrounding medium, creating a sound wave that travels outward.
当物体振动时就会产生声音，例如扬声器纸盆、吉他弦或声带。这些振动扰动周围介质，产生向外传播的声波。
The speed of sound depends 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 transmitted more quickly.
声音的速度取决于介质。一般来说，声音在固体中最快，在液体中较慢，在气体中最慢。这是因为固体中粒子靠得更近，振动能更快地传递。
3. Speed of Sound in Air | 空气中的声速
In air at room temperature (about 20 °C), the speed of sound is approximately 343 m/s. You should remember this value for GCSE calculations. The speed increases with temperature because warmer air has faster-moving particles.
在室温（约 20 °C）的空气中，声速约为 343 m/s。你应该记住这个数值以进行 GCSE 的计算。温度升高时声速增加，因为较热的空气中粒子运动更快。
| Medium | Speed of Sound (m/s) | 介质 | 声速（m/s） |
|---|---|---|---|
| Air (20 °C) | ~343 | 空气 (20°C) | 约 343 |
| Water | ~1500 | 水 | 约 1500 |
| Steel | ~5000 | 钢 | 约 5000 |
4. Wave Equation for Sound | 声音的波动方程
The relationship between wave speed (v), frequency (f), and wavelength (λ) is given by the wave equation:
波速（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 is in hertz (Hz), and λ is in metres (m). You can rearrange this to find any one quantity if the other two are known.
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）。如果已知另外两个量，你可以重新排列公式求出任一量。
For example, a sound wave with frequency 500 Hz and wavelength 0.68 m has speed v = 500 × 0.68 = 340 m/s.
例如，频率为 500 Hz、波长为 0.68 m 的声波，其速度 v = 500 × 0.68 = 340 m/s。
5. Frequency, Pitch and Human Hearing | 频率、音调与人耳听觉
The frequency of a sound wave determines its pitch. A high frequency (short wavelength) corresponds to a high pitch, while a low frequency (long wavelength) corresponds to a low pitch. The amplitude of the wave determines the loudness.
声波的频率决定其音调。高频率（短波长）对应高音调，低频率（长波长）对应低音调。波的振幅决定响度。
The human ear can detect sounds in the frequency range approximately from 20 Hz to 20 000 Hz (20 kHz). Frequencies above this range are called ultrasound, and frequencies below are called infrasound.
人耳能听到的声音频率范围大约在 20 Hz 到 20 000 Hz（20 kHz）之间。高于此范围的频率称为超声波，低于此范围的频率称为次声波。
6. Oscilloscope Traces | 示波器波形图
An oscilloscope displays a sound wave as a voltage–time graph. The horizontal axis represents time, and the vertical axis represents amplitude. From the trace, you can measure the time period (T) and calculate the frequency (f = 1/T).
示波器将声波显示为电压 – 时间图。横轴表示时间，纵轴表示振幅。从波形图中，你可以测量周期（T）并计算频率（f = 1/T）。
A higher frequency wave shows more complete cycles in the same time interval on the screen, while a louder sound gives a greater amplitude (taller peaks).
频率较高的声波在屏幕上相同时间间隔内显示更多完整周期，而更响的声音则具有更大的振幅（更高的波峰）。
7. Echoes and Reflection of Sound | 回声与声音的反射
Sound waves can be reflected by hard surfaces, producing an echo. The time delay between the original sound and its echo can be used to measure distances, such as the depth of a seabed using sonar.
声波可以被硬表面反射，产生回声。原声与回声之间的时间延迟可用来测量距离，例如用声呐测量海底深度。
If the time taken for a sound pulse to travel to a wall and back is t, then the distance to the wall is d = (v × t) / 2, because the sound travels twice the distance.
如果声脉冲传到墙壁并返回所用的时间为 t，那么到墙壁的距离为 d = (v × t) / 2，因为声音走了两倍的路程。
8. Ultrasound: Properties and Uses | 超声波：性质与用途
Ultrasound refers to sound waves with frequencies above 20 000 Hz, beyond the range of human hearing. It can be generated using electronic devices and directed in narrow beams because of its short wavelength.
超声波指频率超过 20 000 Hz、超出人类听觉范围的声波。它可以通过电子设备产生，并由于波长短而能以窄束定向传播。
Common uses of ultrasound include medical imaging (prenatal scans), industrial fault detection, and cleaning delicate objects. In a sonogram, ultrasound pulses reflect off boundaries between different tissues to build up an image.
超声波的常见用途包括医学成像（产前检查）、工业探伤以及清洗精密物体。在声像图中，超声波脉冲在不同组织之间的边界反射，从而构建出图像。
9. Infrasound and Animal Communication | 次声波与动物交流
Infrasound is sound with frequencies below 20 Hz. It is produced by natural events such as earthquakes and volcanoes, and by large machinery. Some animals, like elephants and whales, use infrasound for long-distance communication.
次声波是频率低于 20 Hz 的声音。它由地震、火山等自然事件以及大型机械产生。一些动物，如大象和鲸鱼，利用次声波进行远距离交流。
Because low-frequency sounds can travel great distances with little attenuation, infrasound is useful for monitoring volcanic activity and detecting nuclear tests.
由于低频声音在衰减很小的情况下可以传播很远的距离，次声波对于监测火山活动和探测核试验非常有用。
10. Structure of the Ear | 耳朵的结构
The human ear converts sound vibrations into electrical signals interpreted by the brain. The outer ear collects sound and directs it through the ear canal to the eardrum, causing it to vibrate.
人耳将声音振动转化为大脑可以解读的电信号。外耳收集声音，并通过耳道将其导向鼓膜，使鼓膜振动。
These vibrations are passed through the ossicles (hammer, anvil, stirrup) to the cochlea, where tiny hair cells convert the mechanical vibrations into nerve impulses. The auditory nerve then carries the signals to the brain.
这些振动通过听小骨（锤骨、砧骨、镫骨）传到耳蜗，耳蜗中的微小毛细胞将机械振动转化为神经冲动。然后听神经将信号传递到大脑。
11. Loudness, Amplitude and Energy | 响度、振幅与能量
Loudness is a subjective sensation that depends on the amplitude of a sound wave. A greater amplitude means that more energy is being transferred by the wave, and it will be perceived as louder.
响度是一种主观感觉，取决于声波的振幅。振幅越大，意味着波传递的能量越多，人们感觉声音越响。
However, the relationship between intensity (energy per unit area per second) and amplitude is quadratic: if the amplitude doubles, the energy transferred per second quadruples.
然而，强度（单位面积单位时间的能量）与振幅之间的关系是平方关系：如果振幅加倍，每秒传递的能量变为原来的四倍。
12. The Decibel Scale and Hearing Damage | 分贝标度与听力损伤
Sound intensity level is measured in decibels (dB). The threshold of hearing is 0 dB, while a whisper is about 30 dB, normal conversation is 60 dB, and a rock concert can exceed 110 dB. Prolonged exposure to sound levels above 85 dB can cause permanent hearing damage.
声强级以分贝（dB）来衡量。听觉阈值为 0 dB，低语约 30 dB，正常交谈为 60 dB，摇滚音乐会可能超过 110 dB。长时间暴露在超过 85 dB 的声级下会导致永久性听力损伤。
Loud noises can damage the delicate hair cells in the cochlea, and once destroyed, these cells do not regenerate. This is why wearing ear protection in noisy environments is essential.
巨大的噪音会损伤耳蜗中脆弱的毛细胞，这些细胞一旦被破坏便无法再生。这就是为什么在嘈杂环境中佩戴听力保护装置至关重要。
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