Sound | 声

📚 Sound | 声

Sound is a form of energy produced by vibrating objects. It travels as longitudinal waves through a medium, and its properties – pitch, loudness, and speed – are determined by the frequency, amplitude, and nature of the medium. In the IGCSE CCEA Science specification, understanding sound is essential for grasping wave behaviour, the functioning of the human ear, and practical applications such as ultrasound and noise control.

声音是由振动着的物体产生的一种能量形式。它作为纵波通过介质传播，其音调、响度和速度等特性由频率、振幅和介质的性质决定。在IGCSE CCEA科学大纲中，理解声音对于掌握波动行为、人耳工作原理以及超声和噪声控制等实际应用至关重要。

1. Production of Sound | 声音的产生

Sound is produced when an object vibrates. These vibrations cause the surrounding particles in a medium to move back and forth, creating regions of compression and rarefaction that travel away from the source. For example, a tuning fork vibrates after being struck, and a loudspeaker cone moves rapidly in and out to produce sound.

声音是在物体振动时产生的。这些振动使周围介质中的粒子来回运动，形成压缩区和稀疏区，从而从声源向外传播。例如，音叉被敲击后会振动，扬声器纸盆快速前后运动来发声。

In musical instruments, sound is generated in different ways: string instruments (like a guitar) produce sound through vibrating strings, wind instruments (like a flute) use vibrating air columns, and percussion instruments (like a drum) rely on the vibration of a stretched membrane.

在乐器中，声音以不同方式产生：弦乐器（如吉他）通过琴弦振动发声，管乐器（如长笛）利用空气柱振动，打击乐器（如鼓）则依赖于张紧膜片的振动。

The common factor is always a mechanical vibration. Without vibration, there is no sound.

共同点总是机械振动。没有振动就没有声音。

---

2. Transmission of Sound | 声音的传播

Sound waves are longitudinal waves, meaning the particle displacement is parallel to the direction of wave travel. They consist of alternating compressions (high-pressure regions) and rarefactions (low-pressure regions). Sound cannot travel through a vacuum because there are no particles to transmit the vibrations. This is often demonstrated by placing a ringing bell inside a vacuum chamber – as the air is removed, the sound fades away.

声波是纵波，这意味着粒子的位移方向与波的传播方向平行。声波由交替的压缩区（高压区）和稀疏区（低压区）组成。声音不能在真空中传播，因为没有粒子来传递振动。通常将电铃放在真空罩内演示——随着空气抽出，声音逐渐消失。

Sound can travel through solids, liquids, and gases. The particles must be able to collide with each other and pass on the vibration. In general, sound travels fastest in solids because the particles are closer together, allowing vibrations to be transferred more quickly.

声音可以通过固体、液体和气体传播。粒子必须能够相互碰撞并传递振动。通常，声音在固体中传播最快，因为固体中粒子排列更紧密，振动能更快地传递。

---

3. Speed of Sound | 声速

The speed of sound depends on the medium through which it travels. In air at room temperature (20 °C), the speed of sound is approximately 340 m/s. It is faster in liquids (about 1500 m/s in water) and even faster in solids (about 5000 m/s in steel). The speed increases with the stiffness of the medium and decreases with density.

声速取决于其传播的介质。在室温（20 °C）的空气中，声速约为340 m/s。在液体中更快（水中约1500 m/s），在固体中则更快（钢中约5000 m/s）。声速随介质的刚性增加而增大，随密度增加而减小。

Medium	Speed of sound (m/s)
Air (20 °C)	~340
Water	~1500
Steel	~5000

The relationship between speed (v), frequency (f), and wavelength (λ) for any wave is given by the wave equation: v = f × λ. For sound, this equation can be used to calculate any one of these quantities when the other two are known.

对于任何波，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。对于声音，当已知其他两个量时，可以利用该公式计算第三个量。

---

4. Pitch and Frequency | 音调与频率

The pitch of a sound is how high or low it seems to a listener, and it is determined by the frequency of the sound wave. Frequency is measured in hertz (Hz), where 1 Hz = 1 vibration per second. A high-frequency wave produces a high-pitched sound (e.g., a whistle), while a low-frequency wave produces a low-pitched sound (e.g., a bass drum).

音调是指听者感觉到的声音高低，它由声波的频率决定。频率以赫兹（Hz）为单位，1 Hz = 每秒振动1次。高频波产生高音调声音（如哨声），低频波产生低音调声音（如大鼓）。

On an oscilloscope, a sound with a higher frequency is shown with more wave cycles across the screen in the same time interval, meaning a shorter wavelength for the same wave speed.

在示波器上，频率较高的声音在相同时间间隔内显示更多的波形周期，这意味着在相同波速下波长更短。

The human ear can detect frequencies from about 20 Hz to 20 000 Hz. Sounds below 20 Hz are called infrasound, and those above 20 000 Hz are ultrasound.

人耳可以检测到大约20 Hz到20 000 Hz的频率。低于20 Hz的声音称为次声波，高于20 000 Hz的声音称为超声波。

---

5. Loudness and Amplitude | 响度与振幅

Loudness is the perception of the energy carried by a sound wave. It is directly related to the amplitude of the wave: a larger amplitude means a louder sound. Amplitude is the maximum displacement of particles from their rest position. For the same frequency, increasing the amplitude makes the sound appear louder to our ears.

响度是对声波所携带能量的感知。它直接与波的振幅相关：振幅越大，声音越响亮。振幅是粒子偏离平衡位置的最大位移。对于相同频率，增大振幅会使我们感觉声音更响。

On an oscilloscope trace, a louder sound produces a taller wave (greater peak-to-peak vertical height), whereas a quieter sound shows a shorter wave.

在示波器轨迹上，较响的声音产生的波形更高（从波峰到波谷的垂直高度更大），而较轻的声音波形较短。

Loudness is measured in decibels (dB). Prolonged exposure to sounds above 85 dB can cause hearing damage.

响度以分贝（dB）为单位测量。长时间暴露在85 dB以上的声音中会导致听力损伤。

---

6. Sound Waveforms and the Oscilloscope | 声音的波形与示波器

A cathode-ray oscilloscope (CRO) is a device that can display sound waves as a voltage–time graph. A microphone converts the sound into an electrical signal, and the oscilloscope shows the waveform on the screen. This allows us to visualise and measure the amplitude and frequency of the sound.

阴极射线示波器（CRO）是一种能将声波显示为电压-时间图形的设备。麦克风将声音转换为电信号，示波器则在屏幕上显示波形。这使我们能够观察和测量声音的振幅与频率。

Pure tones (e.g., from a tuning fork) produce smooth, regular sine waves. Noisy or complex sounds (e.g., speech, traffic) produce irregular, jagged waveforms. The quality or timbre of a sound depends on the shape of the waveform, which is why different instruments playing the same note sound different.

纯音（如来自音叉）产生平滑、规则的正弦波。噪音或复杂声音（如说话声、交通噪声）产生不规则、锯齿状的波形。声音的音质或音色取决于波形的形状，这就是为什么不同乐器演奏同一音符听起来不一样。

---

7. Echoes | 回声

An echo is a reflection of sound that arrives at the listener some time after the direct sound. For a distinct echo to be heard, the reflecting surface must be large, flat, and at least 17 m away (assuming the speed of sound is about 340 m/s and the minimum time gap for the brain to distinguish the two sounds is 0.1 s).

回声是声音经反射后到达听者、比直达声晚一些时间到达的现象。要听到清晰回声，反射面必须大而平坦，且距离至少17 m（假设声速约340 m/s，大脑区分两个声音的最小时间间隔为0.1 s）。

Echoes are used in sonar (Sound Navigation and Ranging) systems to measure the depth of the sea or locate objects underwater. The time taken for the echo to return is measured, and the distance can be calculated using: distance = speed × time / 2 (since the sound travels to the object and back).

回声用于声呐（声音导航与测距）系统，以测量海洋深度或定位水下物体。测量回声返回所需的时间，然后利用公式计算距离：距离 = 速度 × 时间 / 2（因为声音往返传播）。

In rooms, unwanted echoes can cause reverberation, which is reduced by using soft furnishings and acoustic panels that absorb sound.

在室内，不希望出现的回声会引起混响，可通过使用柔软的家居装饰和吸声板来减弱混响。

---

8. The Human Ear and Hearing | 人耳与听觉

The human ear is a sensitive organ that converts sound waves into electrical signals for the brain. Sound enters through the outer ear (pinna) and travels along the ear canal to the eardrum (tympanic membrane), causing it to vibrate. These vibrations pass through three tiny bones in the middle ear – the hammer (malleus), anvil (incus), and stirrup (stapes) – which amplify the vibrations and transmit them to the oval window of the cochlea.

人耳是一个将声波转换成电信号传送给大脑的灵敏器官。声音经外耳（耳廓）进入，沿耳道传到鼓膜，使其振动。这些振动通过中耳的三块小骨——锤骨、砧骨和镫骨——放大振动并将其传递到耳蜗的卵圆窗。

Inside the fluid-filled cochlea, the vibrations move tiny hair cells that generate nerve impulses. These impulses travel along the auditory nerve to the brain, where they are interpreted as sound. Damage to hair cells (from loud noise or ageing) leads to permanent hearing loss.

在充满液体的耳蜗内，振动使微小的毛细胞运动，产生神经冲动。这些冲动沿着听神经传到大脑，大脑将其解读为声音。毛细胞受损（由响亮噪声或衰老所致）会导致永久性听力丧失。

The human hearing range is typically 20 Hz to 20 000 Hz, but this range narrows with age, especially at higher frequencies.

人类的听觉范围通常为20 Hz至20 000 Hz，但随着年龄增长，这一范围会缩小，特别是高频部分。

---

9. Ultrasound | 超声波

Ultrasound refers to sound waves with frequencies above 20 000 Hz, beyond the upper limit of human hearing. These high-frequency waves have short wavelengths and can travel in narrow beams, making them useful for scanning and ranging.

超声波是指频率高于20 000 Hz、超出人耳听力上限的声波。这些高频波波长短，能以窄波束形式传播，因此适用于扫描和测距。

In medicine, ultrasound is used for prenatal scanning to produce images of a developing fetus without using harmful ionising radiation. The ultrasound waves reflect off different tissues, and the echoes are used to build a real-time image. Ultrasound is also used to break up kidney stones (lithotripsy) and to clean delicate equipment.

在医学领域，超声波用于产前扫描，在不使用有害电离辐射的情况下生成发育中胎儿的图像。超声波被不同组织反射，其回声用于构建实时图像。超声波还用于击碎肾结石（碎石术）以及清洗精密设备。

In industry, ultrasound can detect flaws in materials (non-destructive testing) and measure thickness. Bats and dolphins use ultrasound for echolocation to navigate and find prey.

在工业领域，超声波可检测材料中的缺陷（无损检测）并测量厚度。蝙蝠和海豚利用超声波进行回声定位，以导航和寻找猎物。

---

10. Noise Pollution and Hearing Protection | 噪音污染与听力保护

Noise pollution is excessive or disturbing sound that can harm human health and the environment. Common sources include traffic, construction, industrial machinery, and loud music. Prolonged exposure to loud noise can lead to stress, sleep disturbance, and permanent hearing loss.

噪音污染是指可能损害人类健康和环境的过度或干扰性声音。常见来源包括交通、建筑施工、工业机械和高声音乐。长时间暴露于噪声中可导致压力、睡眠障碍和永久性听力丧失。

The intensity of sound is measured in decibels (dB). A normal conversation is about 60 dB, while a rock concert can exceed 110 dB. Hearing protection, such as earplugs or earmuffs, should be used in noisy environments. Regulations often require employers to limit workers’ exposure to high noise levels.

声音强度以分贝（dB）衡量。正常交谈约60 dB，摇滚音乐会可超过110 dB。在嘈杂环境中应使用耳塞或耳罩等听力保护装置。法规通常要求雇主限制工人暴露于高噪声水平的时间。

Ways to reduce noise pollution include soundproofing with insulating materials, planting trees as sound barriers, and designing quieter machinery.

减少噪音污染的方法包括使用隔音材料进行隔音、种植树木作为隔声屏障，以及设计更安静的机械。

---

11. Applications and Everyday Phenomena | 应用与日常现象

Sound waves are used in many everyday technologies beyond ultrasound. Microphones convert sound into electrical signals, while loudspeakers do the reverse. Musical instruments rely on standing waves to produce notes of specific frequencies. The design of concert halls uses knowledge of sound reflection and absorption to optimise acoustics.

除超声外，声波还应用于许多日常技术。麦克风将声音转换为电信号，扬声器则相反。乐器依靠驻波产生特定频率的音符。音乐厅的设计利用声音反射和吸收的知识来优化音响效果。

Thunder is heard after lightning because light travels much faster than sound (approximately 3×10⁸ m/s vs. 340 m/s). The time delay between seeing lightning and hearing thunder can be used to estimate the distance of a storm: every 3 seconds of delay corresponds to roughly 1 km.

先看见闪电后听到雷声是因为光速远大于声速（约3×10⁸ m/s对比340 m/s）。看到闪电与听到雷声之间的时间延迟可用于估算风暴距离：每延迟3秒大约对应1 km。

The Doppler effect describes the change in perceived pitch when a sound source moves relative to an observer – a siren sounds higher as it approaches and lower as it moves away. This effect is used in speed cameras and medical blood-flow measurements.

多普勒效应描述了当声源相对于观察者移动时感知音调的变化——警报器靠近时听起来音调较高，远离时较低。此效应用于测速摄像和医学血流测量。

---

Published by TutorHao | IGCSE CCEA Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）