📚 Sound and Hearing Revision | 声音与听力备考专题
This revision guide covers the essential concepts of sound and hearing for the CCEA GCSE Physics specification. Sound waves, their properties, how we hear, and applications such as ultrasound and sonar are all key topics. Understanding these ideas will help you answer exam questions confidently.
本备考指南涵盖 CCEA GCSE 物理大纲中声音与听力的核心概念。声波的性质、人耳如何听到声音，以及超声波和声呐等应用都是关键主题。掌握这些知识将帮助你在考试中自信作答。
1. What is Sound? | 什么是声音？
Sound is a form of energy that travels as longitudinal waves. When an object vibrates, it causes the surrounding medium (such as air) to compress and expand, creating regions of high pressure called compressions and low pressure called rarefactions. These vibrations pass through the medium, carrying energy but not matter.
声音是一种以纵波形式传播的能量。当物体振动时，会使周围介质（如空气）发生压缩和膨胀，形成高压区域（密部）和低压区域（疏部）。这些振动通过介质传播，传递能量而不传递物质。
Sound cannot travel through a vacuum because there are no particles to vibrate. This is why astronauts in space must use radio to communicate. In contrast, light can travel through a vacuum.
声音不能在真空中传播，因为没有粒子可以振动。这就是为什么太空中的宇航员必须使用无线电进行通信。相比之下，光可以在真空中传播。
2. Speed of Sound in Different Media | 声音在不同介质中的速度
The speed of sound depends on the medium through which it travels. In general, sound travels fastest in solids, slower in liquids, and slowest in gases. This is because particles in solids are closer together, allowing vibrations to pass more quickly.
声音的传播速度取决于它所穿过的介质。总的来说，声音在固体中最快，在液体中较慢，在气体中最慢。这是因为固体中的粒子靠得更近，振动传递得更快。
In air at room temperature (20 °C), the speed of sound is approximately 343 m s⁻¹. In water, it is about 1500 m s⁻¹, and in steel, it can be around 5000 m s⁻¹. Knowing these typical values is useful for calculations.
在室温（20 °C）下的空气中，声速约为 343 m s⁻¹。在水中约为 1500 m s⁻¹，在钢铁中可达到约 5000 m s⁻¹。了解这些典型数值有助于进行相关计算。
speed = distance / time (v = d / t)
速度 = 距离 / 时间 (v = d / t)
3. Frequency and Pitch | 频率与音调
Frequency is the number of complete vibrations (or cycles) per second, measured in hertz (Hz). The frequency of a sound wave determines its pitch. A high-frequency wave produces a high-pitched sound, while a low-frequency wave produces a low-pitched sound.
频率是每秒完整振动（或周期）的次数，单位为赫兹（Hz）。声波的频率决定其音调。高频波产生高音调的声音，低频波产生低音调的声音。
The typical human hearing range spans from about 20 Hz to 20 000 Hz (20 kHz). Sounds below 20 Hz are called infrasound, and those above 20 kHz are called ultrasound. Different animals have different hearing ranges; for example, dogs can hear up to about 45 kHz, and bats use ultrasound for navigation.
人类典型的听觉范围约为 20 Hz 到 20 000 Hz（20 kHz）。低于 20 Hz 的声音称为次声波，高于 20 kHz 的声音称为超声波。不同动物的听觉范围不同；例如，狗能听到高达约 45 kHz 的声音，蝙蝠利用超声波进行导航。
4. Amplitude and Loudness | 振幅与响度
Amplitude is the maximum displacement of a wave from its rest position. In a sound wave, a larger amplitude means the wave carries more energy, making the sound louder. Loudness is the human perception of amplitude and is measured in decibels (dB).
振幅是波离开平衡位置的最大位移。在声波中，振幅越大意味着波携带的能量越多，声音就越响。响度是人对振幅的感知，以分贝（dB）为单位测量。
On an oscilloscope trace, a louder sound appears as a wave with greater height (amplitude). A quieter sound has a smaller amplitude. The decibel scale is logarithmic; a 10 dB increase represents a tenfold increase in sound intensity. Prolonged exposure to sounds above 85 dB can damage hearing.
在示波器波形上，较响的声音表现为高度（振幅）更大的波。较安静的声音振幅较小。分贝尺度是对数尺度；增加 10 dB 表示声音强度增加十倍。长时间暴露在高于 85 dB 的声音中会损害听力。
5. The Human Ear and the Process of Hearing | 人耳与听觉过程
The human ear is a complex organ that converts sound waves into electrical signals for the brain. Sound waves enter the outer ear and travel through the ear canal to the eardrum, causing it to vibrate. These vibrations are passed on to three small bones in the middle ear – the hammer, anvil, and stirrup – which amplify the vibrations.
人耳是一个复杂的器官，能将声波转换为大脑可解读的电信号。声波进入外耳，通过耳道到达鼓膜，使其振动。这些振动传递给中耳的三块小骨——锤骨、砧骨和镫骨，它们将振动放大。
The stirrup transfers the vibrations to the oval window of the cochlea, a fluid-filled structure in the inner ear shaped like a snail shell. Inside the cochlea, tiny hair cells move with the fluid, generating electrical signals that travel along the auditory nerve to the brain, where they are interpreted as sound.
镫骨将振动传递给耳蜗的卵圆窗。耳蜗是内耳中一个形似蜗牛壳的充满液体的结构。在耳蜗内部，微小的毛细胞随液体运动，产生电信号，这些信号沿听神经传到大脑，被解读为声音。
The whole process happens extremely quickly, allowing us to respond to sounds in real time. Damage to any part of this system, especially the hair cells, can lead to permanent hearing loss.
整个过程发生得非常快，让我们能够实时对声音做出反应。该系统的任何部分受损，尤其是毛细胞受损，都可能导致永久性听力损失。
6. Hearing Range and Age-Related Loss | 听觉范围与年龄相关的听力损失
A young, healthy person can typically hear frequencies from about 20 Hz to 20 kHz. However, as people age, the upper limit of hearing tends to decrease, a condition known as presbycusis. This is often due to the gradual deterioration of hair cells in the cochlea, especially those that detect higher frequencies.
年轻且健康的人通常能听到大约 20 Hz 到 20 kHz 的频率。然而，随着年龄增长，听力上限往往会下降，这种情况称为老年性听力损失。这通常是由于耳蜗中毛细胞逐渐退化，特别是那些检测较高频率的毛细胞。
Loud music through headphones, frequent exposure to noisy environments, and certain medical conditions can accelerate hearing loss. Using ear protection and keeping the volume at safe levels are important for preserving hearing.
通过耳机听喧闹的音乐、经常暴露在嘈杂环境以及某些疾病都会加速听力损失。使用听力保护装置并将音量控制在安全水平对于保护听力非常重要。
7. Ultrasound: Definition and Applications | 超声波：定义与应用
Ultrasound refers to sound waves with frequencies above the human hearing range, typically above 20 kHz. These waves have many practical applications because they can be directed in narrow beams and can reflect off boundaries between different media.
超声波是指频率超过人类听力范围（通常高于 20 kHz）的声波。这些波有许多实际应用，因为它们可以定向成窄束，并能在不同介质的边界上反射。
In medicine, ultrasound is used for imaging internal body structures, such as checking the development of a fetus during pregnancy. Unlike X-rays, ultrasound does not use ionising radiation, making it safer for both the patient and the unborn baby. Ultrasound can also break down kidney stones and clean delicate equipment.
在医学上，超声波用于身体内部结构成像，例如在怀孕期间检查胎儿发育情况。与 X 射线不同，超声波不使用电离辐射，对患者和未出生的婴儿都更安全。超声波还可用于粉碎肾结石以及清洁精密设备。
In industry, ultrasound can detect flaws in metal structures. High-frequency sound waves are sent into the metal; any crack or defect will reflect the waves back, revealing its location. This is called ultrasonic flaw detection.
在工业上，超声波可以检测金属结构的缺陷。将高频声波射入金属，任何裂缝或缺陷都会将波反射回来，从而显示缺陷位置。这被称为超声探伤。
8. Echo, Reflection and Sonar |
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