IGCSE Edexcel Science: Sound | IGCSE Edexcel 科学：声考点精讲

📚 IGCSE Edexcel Science: Sound | IGCSE Edexcel 科学：声考点精讲

Sound is a form of mechanical energy that propagates as longitudinal waves. Mastering the topic of sound is essential for the IGCSE Edexcel Science examination, as it integrates wave concepts, vibrational sources, and practical applications such as ultrasound imaging and sonar. This article distils the specification into core revision points, explaining each idea clearly in both English and Chinese.

声音是一种以纵波形式传播的机械能。掌握声学专题对 IGCSE Edexcel 科学考试至关重要，因为它融合了波的概念、振动源以及超声成像和声呐等实际应用。本文提炼大纲要点，用中英双语清晰阐述每一个核心概念。

1. Sound waves are longitudinal | 声波是纵波

Sound waves are mechanical longitudinal waves. In a longitudinal wave, the particles of the medium oscillate parallel to the direction of energy transfer. The vibrating object pushes and pulls on the surrounding particles, creating alternating regions of high pressure called compressions and low pressure called rarefactions. It is important to remember that it is the disturbance that travels, not the particles themselves; the particles vibrate about fixed positions.

声波是机械纵波。在纵波中，介质粒子的振动方向与能量传播方向平行。振动物体推拉周围的粒子，形成交替的高压区域（压缩）和低压区域（稀疏）。务必记住，传播的是扰动而非粒子本身；粒子只在固定位置附近振动。

You can visualise a longitudinal wave by thinking of a slinky spring. When you push and pull one end, you see coils bunch together and spread apart along the spring. On an oscilloscope, a pure sound wave is displayed as a transverse trace, but the physical wave in air is longitudinal. The wavelength is the distance from one compression to the next compression.

你可以用螺旋弹簧来想象纵波：推拉一端时，你会看到线圈沿弹簧聚集和散开。在示波器上，一个纯音波显示为横波轨迹，但空气中的实际波动是纵波。波长是两个相邻压缩区之间的距离。

2. Production and the need for a medium | 声的产生与介质需求

Sound is produced by a vibrating source, such as a tuning fork, loudspeaker diaphragm or vocal cords. The vibrations cause the surrounding medium to be alternately compressed and expanded. Sound cannot travel through a vacuum because there are no particles to transmit the vibrations. This is a classic contrast with light, which is an electromagnetic wave and can travel through a vacuum.

声音由振动源产生，例如音叉、扬声器振膜或声带。振动使周围介质交替压缩和膨胀。声音不能在真空中传播，因为没有粒子来传递振动。这是声与光的一个经典区别：光是电磁波，可在真空中传播。

A simple demonstration places an electric bell inside a bell jar. As the air is pumped out, the sound becomes fainter and eventually inaudible, even though the hammer is visibly striking the bell. This proves that a material medium (solid, liquid or gas) is necessary for sound transmission. The particles need to be close enough to pass on the kinetic energy.

一个简单的实验是将电铃放在钟罩内。当空气被抽出时，铃声逐渐减弱，最后听不见，即使可以看见铃锤仍在敲击。这证明声音传播需要物质介质（固、液、气）。粒子必须足够靠近才能传递动能。

3. Speed of sound and the wave equation | 声速与波动方程

The speed of sound depends on the medium and its temperature. In air at room temperature (20 °C), the speed is approximately 340 m/s. Sound travels faster in liquids than in gases, and fastest in solids, because particles are closer together and can pass vibrations more rapidly. The wave equation links speed (v), frequency (f) and wavelength (λ):

声速取决于介质及其温度。在室温 (20 °C) 的空气中，声速约为 340 m/s。声音在液体中比在气体中快，在固体中最快，因为粒子排列更紧密，能更迅速地传递振动。波动方程将速度 (v)、频率 (f) 和波长 (λ) 联系起来：

v = f λ

For any given medium, if the frequency of the sound increases, the wavelength must decrease to keep the speed constant. Typical calculations ask you to find the wavelength of a sound of known frequency, or to calculate the distance travelled in a given time. You should be comfortable rearranging the equation to f = v / λ or λ = v / f.

对于给定介质，若声音频率增大，波长必然减小，以保持速度恒定。典型计算题要求你根据已知频率求波长，或计算在给定时间内声音传播的距离。你应能熟练地将方程变形为 f = v / λ 或 λ = v / f。

4. Frequency determines pitch | 频率决定音调

Frequency is the number of complete vibrations or oscillations per second, measured in hertz (Hz). A high‑frequency sound wave produces a high‑pitched note, while a low‑frequency wave gives a low‑pitched note. The frequency of a sound depends on the source’s vibration rate: a tightly stretched string, a short tube or a small drumhead tends to vibrate faster and produces a higher pitch.

频率是每秒完整振动的次数，单位为赫兹 (Hz)。高频声波产生高音调，低频声波则产生低音调。声音的频率取决于声源的振动速率：紧绷的弦、短管或小鼓面往往振动较快，产生较高音调。

On an oscilloscope trace, frequency is shown by how many complete waves fit into a given time division. If the time base is set to, say, 1 ms per division, you can determine the period T of one wave and then use f = 1/T. A higher frequency trace appears more ‘squashed’ horizontally, with more cycles visible across the screen.

在示波器轨迹上，频率表现为给定时间刻度内完整波的数量。若时基设为例如每格 1 ms，你可以测定一个波的周期 T，然后用 f = 1/T 求频率。频率较高的波形看起来水平方向更“压缩”，屏幕上可见更多周期。

5. Amplitude decides loudness | 振幅决定响度

The amplitude of a sound wave is the maximum displacement of particles from their undisturbed position. A larger amplitude transfers more energy and makes the sound louder. Loudness is a subjective sensation; the objective physical measure is sound intensity, often expressed in decibels (dB). On an oscilloscope, a louder sound produces a trace with taller peaks and deeper troughs.

声波的振幅是粒子偏离其平衡位置的最大位移。振幅越大，传递的能量越多，声音越响。响度是主观感受，客观的物理量度是声强，常用分贝 (dB) 表示。在示波器上，更响的声音产生的波形峰更高、谷更深。

It is important not to confuse amplitude with frequency. A sound can be loud and low‑pitched (large amplitude, low frequency) or quiet and high‑pitched (small amplitude, high frequency). Changes in amplitude do not alter the speed or frequency of the wave in a given medium.

切勿混淆振幅和频率。声音可以又响又低沉（大振幅、低频率），也可以轻而尖锐（小振幅、高频率）。在给定介质中，振幅的变化不改变波速或频率。

6. Oscilloscope wave forms | 示波器波形

A cathode‑ray oscilloscope (CRO) connected to a microphone displays sound signals as transverse wave traces. A pure musical tone from a tuning fork or a signal generator shows a smooth, regular sine wave. Noise or a complex musical chord gives an irregular, jagged pattern without a clear single frequency. The oscilloscope allows us to measure amplitude (peak voltage) and Period.

连接到麦克风的阴极射线示波器 (CRO) 会将声音信号显示为横波轨迹。音叉或信号发生器发出的纯乐音展现平滑、规则的正弦波。噪声或复杂的和弦则呈现无规则、参差不齐的波形，没有单一清晰的频率。示波器使我们能测量振幅（峰值电压）和周期。

When comparing two sounds, you can see the difference in frequency by counting cycles per division, and the difference in amplitude by the vertical height. A microphone converts the sound energy into an electrical signal that mirrors the pattern of compressions and rarefactions.

比较两种声音时，你可以通过计算每格内的周期数看出频率差异，通过垂直高度看出振幅差异。麦克风将声能转换为电信号，其波形镜像反映压缩与稀疏的模式。

7. Human hearing and ultrasound | 人耳听觉范围与超声波

The average human ear can detect sound frequencies from about 20 Hz to 20 000 Hz (20 kHz). Sounds below 20 Hz are called infrasound, and those above 20 kHz are ultrasound. As people age, the upper limit often drops; high‑frequency hearing loss is common. Many animals, such as bats and dolphins, can produce and hear ultrasound.

人耳平均可听到约 20 Hz 至 20 000 Hz (20 kHz) 的声音。低于 20 Hz 的称为次声波，高于 20 kHz 的称为超声波。随着年龄增长，听力上限通常会下降；高频听力损失很普遍。蝙蝠、海豚等许多动物能发出并听到超声波。

Ultrasound has numerous applications. In medicine, it is used for prenatal scanning (ultrasonography) because it reflects from boundaries between different tissues without the ionising radiation of X‑rays. In industry, ultrasound can detect hidden flaws in metals. Sonar systems also employ ultrasound to map the seafloor or locate fish schools.

超声波有众多应用。医学上，它用于产前扫描（超声波检查法），因为它能在不同组织界面反射，且没有 X 射线的电离辐射。工业上，超声波可探测金属内部缺陷。声呐系统也利用超声波绘制海床地图或探测鱼群。

8. Echoes and sonar ranging | 回声与声呐测距

When sound waves strike a large, hard surface, they are reflected, creating an echo. The time delay between the original sound and its echo can be used to determine the distance to the reflecting surface. Since the sound travels to the surface and back, the total distance is 2d, where d is the one‑way distance. The formula used is:

当声波遇到大而坚硬的表面时会被反射，产生回声。通过原声与回声之间的时间延迟，可以推算反射面的距离。由于声音往返于表面，总距离是 2d，其中 d 为单程距离。使用的公式如下：

d = (v × t) / 2

Here v is the speed of sound in the medium and t is the echo delay time. Sonar (Sound Navigation And Ranging) employs this principle underwater using high‑frequency ultrasound pulses. The same idea is used by bats for echolocation and by ships to measure sea depth.

此式中 v 是该介质中的声速，t 是回声延迟时间。声呐（声音导航与测距）在水下利用高频超声波脉冲实现这一原理。蝙蝠的回声定位以及船只测量海水深度也使用了相同的方法。

9. Transmission through different media | 不同介质中的传播

Sound travels at different speeds in solids, liquids and gases. In general, the speed is fastest in solids (e.g., steel ~5000 m/s), slower in liquids (e.g., water ~1500 m/s) and slowest in gases (air ~340 m/s). This is because particles in a solid are tightly bonded and can quickly pass the vibrational energy. The closer the particles, the more efficiently compressions and rarefactions are transmitted.

声音在固、液、气体中的传播速度不同。通常，固体中最快（如钢铁约 5000 m/s），液体中较慢（如水约 1500 m/s），气体中最慢（空气约 340 m/s）。这是因为固体粒子结合紧密，能迅速传递振动能量。粒子越紧密，压缩与稀疏的传递效率就越高。

Density and stiffness both play a role. Although sound travels slower in air, we rely on air as the primary medium for speech and hearing. You may be asked to compare the speed in different substances using the order solid > liquid > gas, or to explain an experiment that shows sound travelling through a string telephone.

材料的密度和刚度都起作用。尽管声音在空气中传播较慢，但我们依赖空气作为说话和听觉的主要介质。考题可能要求你按固体 > 液体 > 气体的顺序比较速度，或解释一个证明声音通过“土电话”传播的实验。

10. Reflection, absorption and transmission | 声的反射、吸收与透射

When sound encounters an obstacle, some of its energy is reflected, some is absorbed and some may be transmitted through the material. Smooth, hard surfaces like concrete or metal reflect most of the sound, causing echoes. Soft, porous materials such as carpets, curtains and foam absorb sound energy, converting it into heat. Absorption reduces echoes and noise.

当声音遇到障碍物时，部分能量被反射，部分被吸收，还有一部分可能穿过材料透射出去。光滑坚硬的表面如混凝土或金属会反射大部分声音，产生回声。柔软、多孔的材料如地毯、窗帘和泡沫则吸收声能，将其转化为热。吸收可以减少回声和噪音。

This principle is used in soundproofing studios and concert halls. Heavy curtains and acoustic tiles absorb sound, while angled panels diffuse reflections. Understanding how materials interact with sound helps in designing spaces with good acoustics and in controlling unwanted noise.

这一原理用于录音棚和音乐厅的隔音。厚重的幕帘和吸音板吸收声音，而有角度的面板则扩散反射。了解材料与声音的相互作用有助于设计声学良好的空间，也有助于控制恼人的噪音。

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

更多咨询请联系16621398022（同微信）

IGCSE Edexcel Science: Sound | IGCSE Edexcel 科学：声 考点精讲