📚 IGCSE CCEA Physics: Waves - Key Points | IGCSE CCEA 物理：波 考点精讲
Waves transfer energy from one place to another without transferring matter. In the IGCSE CCEA Physics specification, understanding wave properties, wave behaviour and the electromagnetic spectrum is essential. This article summarises the core concepts, equations and experimental contexts you need for your exam.
波将能量从一个地方传递到另一个地方，而不传递物质。在 IGCSE CCEA 物理大纲中，理解波的性质、波的传播行为以及电磁波谱至关重要。本文总结了考试所需的核心概念、公式和实验背景。
1. Types of Waves | 波的种类
Waves are classified as transverse or longitudinal based on the direction of particle oscillation relative to the direction of energy transfer.
根据粒子振动方向与能量传递方向的相对关系，波分为横波和纵波。
In transverse waves, particles oscillate perpendicular to the direction of energy travel. Examples include light, water waves and all electromagnetic waves.
在横波中，粒子振动方向与能量传播方向垂直。例如光、水波和所有电磁波。
In longitudinal waves, particles oscillate parallel to the direction of energy travel. Sound waves in air are longitudinal, consisting of compressions and rarefactions.
在纵波中，粒子振动方向与能量传播方向平行。空气中的声波是纵波，由压缩区和稀疏区组成。
2. Wave Parameters | 波的参数
You must be able to describe and identify the following quantities on a wave diagram.
你必须能够在波形图上描述和识别以下物理量。
Amplitude – the maximum displacement of a point on the wave from its undisturbed position. It relates to the energy carried by the wave.
振幅——波上某点离开平衡位置的最大位移。它与波携带的能量有关。
Wavelength (λ) – the distance between two consecutive points that are in phase, e.g. crest to crest or compression to compression.
波长 (λ)——两个相邻同相点之间的距离，例如波峰到波峰或压缩区到压缩区。
Frequency (f) – the number of complete waves passing a point per second, measured in hertz (Hz).
频率 (f)——每秒通过某点的完整波数，单位为赫兹 (Hz)。
Period (T) – the time taken for one complete wave to pass a point. T = 1/f.
周期 (T)——一个完整波通过某点所需的时间。T = 1/f。
Wave speed (v) – the distance travelled by the wave per unit time.
波速 (v)——波在单位时间内传播的距离。
3. The Wave Equation | 波速公式
The speed of a wave is related to its frequency and wavelength by the equation:
波速与频率和波长之间的关系由以下公式给出：
v = f × λ
where v is wave speed in metres per second (m/s), f is frequency in hertz (Hz), and λ is wavelength in metres (m).
其中 v 为波速（米/秒），f 为频率（赫兹），λ 为波长（米）。
This equation applies to all types of waves, including sound, water waves and electromagnetic waves.
该公式适用于所有类型的波，包括声波、水波和电磁波。
When using the equation, make sure to convert units correctly, e.g. kHz to Hz, cm to m.
使用公式时，务必正确转换单位，例如千赫兹转为赫兹，厘米转为米。
4. Reflection of Waves | 波的反射
Reflection occurs when a wave bounces off a surface and changes direction. The angle of incidence equals the angle of reflection, measured from the normal.
当波从表面反弹并改变方向时发生反射。入射角等于反射角，均从法线量度。
Ripple tank experiments with a straight barrier show circular or plane waves reflecting according to the law of reflection.
用直障碍物在波纹槽中实验，可观察到圆形波或平面波的反射遵循反射定律。
Sound echoes and mirror images are everyday examples of wave reflection.
回声和镜面成像是波反射的日常例子。
The wave speed, frequency and wavelength remain unchanged during reflection, since the medium does not change.
由于介质不变，反射过程中波速、频率和波长保持不变。
5. Refraction of Waves | 波的折射
Refraction is the change in direction of a wave when it enters a new medium at an angle, caused by a change in wave speed.
折射是波以一定角度进入新介质时，由于波速改变而引起的方向变化。
When water waves move from deep to shallow water, their speed decreases, wavelength shortens and they bend towards the normal.
当水波从深水区进入浅水区时，波速减小，波长变短，波向法线方向偏折。
Frequency remains constant during refraction because it is determined by the source.
折射过程中频率保持不变，因为频率由波源决定。
Refraction can be demonstrated clearly in a ripple tank using a glass plate to create a shallow region.
在波纹槽中，用玻璃板制造浅水区域，可清晰地演示折射。
6. Diffraction of Waves | 波的衍射
Diffraction is the spreading out of waves when they pass through a gap or around an obstacle. It is most noticeable when the gap width is similar to the wavelength.
衍射是波通过缝隙或绕过障碍物时发生的扩散现象。当缝隙宽度与波长相近时，衍射最为明显。
If the gap is much larger than the wavelength, the wave passes through with minimal spreading.
若缝隙远大于波长，波通过时扩散很小。
If the gap is comparable to the wavelength, the wave spreads out almost in a semicircle.
若缝隙与波长相当，波几乎以半圆形扩散开来。
Diffraction explains why we can hear sounds around corners but do not see sharp shadows for light under ordinary conditions (since visible light has a much smaller wavelength).
衍射解释了为何我们能听到拐角处的声音，而通常看不到光的明显衍射（因为可见光波长极短）。
7. Sound Waves | 声波
Sound is a longitudinal wave that requires a medium to travel. It cannot propagate through a vacuum.
声音是一种需要介质传播的纵波，无法在真空中传播。
The speed of sound in air is approximately 330 m/s at room temperature; it is faster in liquids and even faster in solids.
室温下声音在空气中的速度约为330 m/s；在液体中更快，在固体中最快。
An oscilloscope can display sound wave signals, allowing measurement of frequency and amplitude.
示波器可显示声波信号，从而测量频率和振幅。
Pitch relates to frequency; loudness relates to amplitude.
音调与频率有关；响度与振幅有关。
In ultrasound, frequencies above 20 000 Hz are used for medical imaging and industrial cleaning.
超声波（频率高于20 000 Hz）用于医学成像和工业清洁。
8. Electromagnetic Waves | 电磁波
10⁸ m/s. The EM spectrum, in order of increasing frequency and decreasing wavelength, is:
电磁波是可以在真空中以 3.0 × 10⁸ m/s 传播的横波。按频率递增、波长递减的顺序，电磁波谱为：
| Region | Approximate wavelength range | Uses / Properties |
|---|---|---|
| Radio waves | > 0.1 m | Broadcasting, communications |
| Microwaves | 0.1 m – 1 mm | Satellite communication, cooking |
| Infrared | 1 mm – 700 nm | Thermal imaging, remote controls |
| Visible light | 700 nm – 400 nm | Vision, optical fibres |
| Ultraviolet | 400 nm – 10 nm | Sun tanning, fluorescence, sterilisation |
| X-rays | 10 nm – 0.01 nm | Medical imaging, security |
| Gamma rays | < 0.01 nm | Cancer treatment, sterilisation |
um All EM waves share the same speed in vacuum but have different wavelengths and frequencies, and they obey the wave equation v = fλ.
所有电磁波在真空中的速度相同，但波长和频率不同，且均遵循波速公式 v = fλ。
9. Light: Reflection and Refraction | 光的反射与折射
Light behaves as a transverse wave and undergoes both reflection and refraction.
光表现为横波，会发生反射和折射。
Reflection from a plane mirror produces an upright, virtual image that is the same size as the object and located behind the mirror.
平面镜反射生成正立、等大的虚像，且像位于镜后。
sin r, where i is the angle of incidence in vacuum (air) and r is the angle of refraction.
当光从空气进入玻璃时，速度减慢并向法线偏折。材料的折射率 n 由 n = sin i / sin r 给出，其中 i 为真空中（空气）的入射角，r 为折射角。
The speed of light in a medium is v = c / n, where c = 3.0 × 10⁸ m/s.
介质中的光速为 v = c / n，其中 c = 3.0 × 10⁸ m/s。
Practical work often involves tracing ray paths with pins and measuring angles with a protractor.
实验常通过插针法描绘光路，用量角器测量角度。
10. Total Internal Reflection | 全内反射
Total internal reflection (TIR) occurs when light travels from a denser medium to a less dense medium at an angle of incidence greater than the critical angle.
当光从光密介质射向光疏介质，且入射角大于临界角时，发生全内反射。
1 / n, where n is the refractive index of the denser medium relative to the rarer medium.
临界角 c 满足 sin c = 1 / n，其中 n 为光密介质相对于光疏介质的折射率。
Optical fibres use TIR to transmit light signals over long distances with very little loss. They are essential in telecommunications and endoscopy.
光纤利用全内反射以极低损耗远距离传输光信号，是电信和内窥镜检查的关键技术。
You should be able to explain the conditions for TIR and calculate the critical angle given the refractive index.
你应该能解释全内反射的条件，并在给定折射率的情况下计算临界角。
11. Properties of Electromagnetic Waves and Applications | 电磁波的性质与应用
Different regions of the EM spectrum have specific properties and applications, which you should be able to recall and explain.
电磁波谱的不同区域具有特定的性质和应用，你需要能够记忆并解释。
Radio waves: used for TV and radio broadcasting because they can be reflected by the ionosphere and diffract around hills.
无线电波：用于电视和广播，因为它们可被电离层反射并能绕山衍射。
Microwaves: used for satellite communication and in microwave ovens; water molecules absorb microwave energy strongly.
微波：用于卫星通信和微波炉；水分子强烈吸收微波能量。
Infrared: emitted by warm objects; used in heaters and infrared cameras.
红外线：由热物体发出；用于加热器和红外摄像机。
Ultraviolet: can cause skin tanning and damage; used in fluorescent lamps and to kill bacteria.
紫外线：可晒黑皮肤并造成损伤；用于荧光灯和杀菌。
X-rays and gamma rays: high-energy ionising radiation used for medical imaging and cancer therapy, but require careful safety precautions.
X 射线和伽马射线：高能电离辐射，用于医学成像和癌症治疗，但需要严格的安全防护。
You may be asked to compare the hazards and uses of different EM radiations based on their energy and penetrating power.
你可能会被要求根据能量和穿透力比较不同电磁辐射的危害和用途。
12. Experimental Skills for Waves | 波相关实验技能
CCEA IGCSE Physics often assesses practical understanding of wave topics. You should be familiar with the following key experiments:
CCEA IGCSE 物理常考查对波相关实验的理解。你应熟悉以下关键实验：
Measuring the speed of sound: using echoes, an oscilloscope, or a resonance tube with a tuning fork to determine wavelength and frequency.
测量声速：利用回声、示波器、或使用共振管和音叉测定波长和频率。
Ripple tank water waves. Measure wavelength with a strobe or ruler, and calculate speed using v = fλ.
波纹槽：研究水波的反射、折射和衍射。用频闪仪或尺子测量波长，利用 v = fλ 计算波速。
Refraction of light: trace ray paths through a glass block; measure angles and verify Snell's law. Calculate refractive index.
光的折射：描迹光线通过玻璃块的路径；测量角度并验证斯涅尔定律，计算折射率。
Critical angle and TIR: using a semicircular glass block to find the critical angle and observe total internal reflection.
临界角与全内反射：使用半圆形玻璃块确定临界角并观察全内反射。
Always identify control variables, safety considerations and sources of error in these experiments.
在这些实验中，总要明确控制变量、安全注意事项和误差来源。
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