📚 IGCSE AQA Physics: Waves Topic Review | IGCSE AQA 物理：波 考点精讲
Waves are one of the core topics in IGCSE AQA Physics. A solid understanding of wave properties, the wave equation, the electromagnetic spectrum, and the behaviour of sound and seismic waves is essential for success in both Paper 1 and Paper 2. This article breaks down every key concept with clear explanations, examples, and paired bilingual content to help you master the topic.
波是IGCSE AQA物理的核心主题之一。透彻理解波的性质、波动方程、电磁波谱以及声波和地震波的行为，对于在试卷1和试卷2中取得成功至关重要。本文通过清晰的解释、实例和中英对照内容，帮助你全面掌握这一考点。
1. What is a Wave? | 什么是波？
A wave is a disturbance that transfers energy from one place to another without transferring matter. Waves can travel through a medium (like water or air) or through a vacuum (in the case of electromagnetic waves).
波是一种扰动，它将能量从一个地方传递到另一个地方，而无需传递物质。波可以通过介质（如水或空气）传播，也可以在真空中传播（如电磁波）。
All waves carry energy. The particles in a medium oscillate about fixed positions, but they do not travel with the wave. The energy is what moves forward.
所有波都携带能量。介质中的粒子在固定位置附近振荡，但它们并不随着波一起迁移。向前移动的是能量。
Waves can be classified as either mechanical (requiring a medium) or electromagnetic (able to travel through a vacuum). Sound waves and water waves are mechanical; light and radio waves are electromagnetic.
波可以分为机械波（需要介质）和电磁波（能够在真空中传播）。声波和水波是机械波；光波和无线电波是电磁波。
2. Transverse and Longitudinal Waves | 横波与纵波
In a transverse wave, the vibrations are perpendicular (at right angles) to the direction of energy transfer. Examples include water ripples, all electromagnetic waves, and waves on a guitar string.
在横波中，振动方向与能量传递方向垂直（成直角）。例子包括水面涟漪、所有电磁波以及吉他弦上的波。
In a longitudinal wave, the vibrations are parallel to the direction of energy transfer. Sound waves and seismic P-waves are longitudinal. They consist of compressions (regions of high pressure) and rarefactions (regions of low pressure).
在纵波中，振动方向与能量传递方向平行。声波和地震P波是纵波。它们由压缩区（高压区域）和稀疏区（低压区域）组成。
You should be able to label the amplitude, wavelength, crest, and trough on a transverse wave diagram. For a longitudinal wave, label compressions and rarefactions. The wavelength is the distance between two consecutive crests, troughs, or compressions.
你应该能够在横波图上标出振幅、波长、波峰和波谷。对于纵波，标明压缩区和稀疏区。波长是两个相邻波峰、波谷或压缩区之间的距离。
| Transverse wave | 横波 | Longitudinal wave | 纵波 |
|---|---|---|---|
| Vibrations perpendicular to energy transfer | 振动方向与能量传递方向垂直 | Vibrations parallel to energy transfer | 振动方向与能量传递方向平行 |
| Has crests and troughs | 有波峰和波谷 | Has compressions and rarefactions | 有压缩区和稀疏区 |
3. Wave Properties – Amplitude, Wavelength, Frequency and Period | 波的性质 – 振幅、波长、频率和周期
The amplitude of a wave is the maximum displacement of a point on the wave from its rest position. It relates to the energy carried by the wave: the greater the amplitude, the more energy.
波的振幅是波上某一点离开其平衡位置的最大位移。它与波携带的能量有关：振幅越大，能量越多。
Wavelength (λ) is the distance between two identical points on consecutive waves, such as crest to crest. It is measured in metres (m).
波长（λ）是相邻波上两个相同点（如波峰到波峰）之间的距离。它以米（m）为单位测量。
Frequency (f) is the number of complete waves passing a point per second. It is measured in hertz (Hz). 1 Hz = 1 wave per second.
频率（f）是每秒钟通过某一点的完整波的数目。它以赫兹（Hz）为单位。1 Hz = 每秒1个波。
The period (T) is the time taken for one complete wave to pass a given point. It is measured in seconds (s). The relationship between period and frequency is:
周期（T）是一个完整的波通过某一点所需的时间。它以秒（s）为单位。周期与频率的关系是：
T = 1 / f or f = 1 / T
The number of waves passing per second is the frequency, and the time for one wave is the period. A wave with a frequency of 50 Hz has a period of 0.02 s.
每秒钟通过的波数就是频率，一个波所需的时间就是周期。频率为50 Hz的波，其周期为0.02秒。
4. The Wave Equation | 波动方程
The wave speed (v), frequency (f), and wavelength (λ) are linked by the wave equation:
波速（v）、频率（f）和波长（λ）通过波动方程联系：
v = f × λ
Wave speed is measured in metres per second (m/s), frequency in hertz (Hz), and wavelength in metres (m). This equation applies to all types of wave, including sound, light, and water waves.
波速以米每秒（m/s）为单位，频率以赫兹（Hz）为单位，波长以米（m）为单位。该方程适用于所有类型的波，包括声波、光波和水波。
You can rearrange the equation to f = v / λ or λ = v / f. For example, if a sound wave has a frequency of 440 Hz and a wavelength of 0.75 m, its speed is v = 440 × 0.75 = 330 m/s.
你可以将方程变形为 f = v / λ 或 λ = v / f。例如，如果声波的频率为440 Hz，波长为0.75 m，那么它的波速为 v = 440 × 0.75 = 330 m/s。
When a wave moves from one medium to another, its speed and wavelength may change, but its frequency stays the same. This is because frequency is determined by the source.
当波从一种介质进入另一种介质时，其波速和波长可能改变，但频率保持不变。这是因为频率是由波源决定的。
5. Reflection, Refraction and Transmission | 反射、折射与透射
Waves can be reflected when they hit a boundary. The angle of incidence equals the angle of reflection, measured from the normal (a line perpendicular to the surface). Reflection explains echoes and mirror images.
波遇到边界时会发生反射。入射角等于反射角，它们都是从法线（垂直于表面的线）起测量的。反射现象可解释回声和镜像。
Refraction occurs when a wave changes speed as it crosses a boundary between two media of different densities. This causes the wave to change direction unless it hits the boundary along the normal.
当波在穿过两种不同密度介质的边界时速度发生变化，就会发生折射。除非波沿法线入射，否则波的方向会发生改变。
If a wave slows down entering a denser medium (e.g., light from air into glass), it bends towards the normal. If it speeds up, it bends away from the normal. Sound waves, however, speed up in denser materials.
如果波在进入较密介质时速度变慢（例如光从空气进入玻璃），它会向法线方向偏折。如果速度变快，它会偏离法线。而声波在较密材料中速度变快。
Transmission means the wave passes through a material, often with some absorption. The amount of transmission depends on the material’s properties. Opaque materials absorb or reflect light; transparent materials transmit it.
透射意味着波穿过材料，通常伴有部分吸收。透射量取决于材料的性质。不透明材料吸收或反射光；透明材料能透射光。
6. Diffraction | 衍射
Diffraction is the spreading out of waves as they pass through a gap or around an obstacle. It is most noticeable when the wavelength is roughly the same size as the gap or obstacle. Larger wavelengths produce more diffraction.
衍射是波穿过缝隙或绕过障碍物时发生的扩散现象。当波长与缝隙或障碍物的尺寸大致相当时，衍射最为明显。波长越大，衍射越显著。
Sound waves, which have relatively long wavelengths (a few centimetres to metres), diffract around doors and corners, which is why you can hear someone even if you cannot see them. Light has very short wavelengths, so its diffraction effects are much less obvious in everyday life.
声波的波长相对较长（几厘米到几米），可以绕过门和墙角产生衍射，这就是为什么即使看不到人也能听到声音。光波的波长非常短，因此在日常生活中其衍射效应远没有那么明显。
Diffraction can be demonstrated using a ripple tank with a variable gap. When the gap is wide compared to the wavelength, the wave passes straight through; when the gap is narrowed, the wave spreads out into a semicircular pattern.
衍射可以通过一个带可调缝隙的波纹槽来演示。当缝隙宽度远大于波长时，波直线通过；当缝隙变窄时，波会扩散成一个半圆形图案。
7. The Electromagnetic Spectrum | 电磁波谱
The electromagnetic (EM) spectrum is a family of transverse waves that all travel at the same speed in a vacuum: 3.0 × 10⁸ m/s (the speed of light). They differ in frequency and wavelength. The spectrum, in order of decreasing wavelength (or increasing frequency), is:
电磁波谱是一个横波家族，它们在真空中的速度都相同：3.0 × 10⁸ m/s（光速）。它们的区别在于频率和波长。按照波长递减（或频率递增）的顺序，波谱排列为：
- Radio waves | 无线电波
- Microwaves | 微波
- Infrared (IR) radiation | 红外线
- Visible light | 可见光
- Ultraviolet (UV) radiation | 紫外线
- X-rays | X射线
- Gamma rays (γ) | 伽马射线
All EM waves can travel through a vacuum, transfer energy, and obey the same wave equation v = fλ. As you go from radio to gamma, frequency increases, wavelength decreases, and the energy carried by each photon increases.
所有电磁波都能在真空中传播，能够传递能量，并遵循相同的波动方程 v = fλ。从无线电波到伽马射线，频率递增，波长递减，每个光子携带的能量递增。
Remember: The higher the frequency of EM radiation, the more dangerous it is to living cells because of its ionising ability. Gamma rays, X-rays, and ultraviolet are ionising; radio waves, microwaves, and infrared are not.
记住：电磁辐射的频率越高，对活细胞的危害越大，因为它具有电离能力。伽马射线、X射线和紫外线具有电离性；无线电波、微波和红外线则不具有。
8. Uses and Dangers of Electromagnetic Waves | 电磁波的用途与危害
Each region of the EM spectrum has specific practical uses and potential hazards. The table below summarises the key points.
电磁波谱的每个区域都有特定的实际用途和潜在危害。下表总结了关键点：
| EM wave | 电磁波 | Uses | 用途 | Dangers | 危害 |
|---|---|---|---|---|---|
| Radio | 无线电波 | Broadcasting, communications | 广播、通信 | No known health risks for typical exposures | 通常暴露无已知健康风险 |
| Microwaves | 微波 | Cooking, satellite transmissions | 烹饪、卫星传输 | Internal heating of body tissue | 人体组织内部加热 |
| Infrared | 红外线 | Heaters, night vision, remote controls | 加热器、夜视仪、遥控器 | Skin burns | 皮肤灼伤 |
| Visible light | 可见光 | Seeing, photography, optical fibres | 视觉、摄影、光纤 | Bright light can damage retina | 强光可损伤视网膜 |
| Ultraviolet | 紫外线 | Sun tan beds, fluorescent lamps, disinfection | 日光浴、荧光灯、消毒 | Skin cancer, eye damage (ionising) | 皮肤癌、眼睛损伤（电离性） |
| X-rays | X射线 | Medical imaging, airport security | 医学成像、机场安检 | Cell mutation, cancer (ionising) | 细胞突变、癌症（电离性） |
| Gamma | 伽马射线 | Cancer treatment, sterilising equipment | 癌症治疗、设备消毒 | Severe cell damage, genetic mutation (ionising) | 严重细胞损伤、基因突变（电离性） |
In the exam, you will often be asked to link a specific wave to its application and to explain why it is suitable based on its properties (e.g., microwaves are used for satellite communication because they can penetrate the atmosphere).
在考试中，你常常需要将特定的波与其应用联系起来，并根据其性质解释其适用性（例如，微波用于卫星通信，因为它们能够穿透大气层）。
9. Sound Waves | 声波
Sound waves are longitudinal mechanical waves. They need a medium to travel through – they cannot travel through a vacuum. The particles vibrate parallel to the direction of the wave, forming compressions and rarefactions.
声波是纵机械波。它们需要介质才能传播——不能在真空中传播。粒子平行于波的方向振动，形成压缩区和稀疏区。
The speed of sound depends on the medium. It travels fastest in solids, slower in liquids, and slowest in gases. In air at 20 °C, the speed of sound is about 340 m/s.
声速取决于介质。在固体中最快，液体中较慢，气体中最慢。在20 °C的空气中，声速大约为340 m/s。
Pitch is determined by frequency: a high-frequency wave gives a high-pitched sound. Loudness is related to the amplitude of the wave: larger amplitude means louder sound. Both can be viewed on an oscilloscope trace.
音调由频率决定：高频波产生高音调的声音。响度与波的振幅有关：振幅越大，声音越响。两者都可以在示波器波形上观察到。
An echo is a reflection of sound. Hard surfaces reflect sound well, producing echoes; soft materials absorb sound, reducing echoes. Ultrasound is sound with frequencies above 20,000 Hz (the upper limit of human hearing) and is used for medical imaging (e.g., foetal scans) and sonar.
回声是声音的反射。硬质表面能很好地反射声音，产生回声；柔软材料吸收声音，减少回声。超声波是频率超过20,000 Hz（人类听觉的上限）的声波，用于医学成像（如胎儿扫描）和声纳。
10. Seismic Waves | 地震波
Seismic waves are generated by earthquakes or explosions. There are two main types: P-waves (primary waves) and S-waves (secondary waves). They provide evidence for the structure of the Earth’s interior.
地震波是由地震或爆炸产生的。主要有两种类型：P波（纵波，主波）和S波（横波，次波）。它们为地球内部结构提供了证据。
P-waves are longitudinal, travel faster, and can pass through both solids and liquids. S-waves are transverse, travel slower, and can only pass through solids. Because S-waves are not detected on the opposite side of the Earth from an earthquake, we infer that the outer core is liquid.
P波是纵波，传播速度较快，并能通过固体和液体。S波是横波，传播速度较慢，并且只能通过固体。由于在地震震中的对面检测不到S波，我们推断地球外核是液态的。
When seismic waves cross a boundary between different layers of rock, they can be refracted or reflected. By monitoring arrival times at different observing stations, scientists can map the structure of the Earth’s mantle, outer core, and inner core.
当地震波穿过不同岩层之间的边界时，会发生折射或反射。通过监测不同观测站的到达时间，科学家可以绘制出地球地幔、外核和内核的结构图。
11. Refraction of Light and Total Internal Reflection | 光的折射与全内反射
When light passes from one transparent medium to another at an angle, it changes speed and bends. Snell’s law can be used to calculate the angles, but for IGCSE AQA you are expected to describe and draw the ray diagrams for refraction.
当光从一个透明介质以某个角度进入另一个透明介质时，其速度发生变化并发生偏折。斯涅尔定律可用于计算角度，但在IGCSE AQA中，你只需描述和绘制折射的光线图。
A light ray entering a denser medium (e.g., from air to glass) bends towards the normal because it slows down. A ray leaving the denser medium accelerates and bends away from the normal.
光线进入更密的介质（如从空气到玻璃）时，因为速度变慢会向法线方向偏折。光线离开更密介质时速度加快，会偏离法线。
Total internal reflection (TIR) occurs when light travelling in a denser medium hits a boundary with a less dense medium at an angle greater than the critical angle. All the light is reflected back inside. This is the principle behind optical fibres and endoscopes.
全内反射（TIR）发生在光在较密介质中传播，并以大于临界角的角度射向与较疏介质的边界上时。所有光都被反射回内部。这就是光纤和内窥镜背后的原理。
The critical angle depends on the two materials. For glass to air, it is around 42°. When the angle of incidence is greater than the critical angle, no light refracts out – it is entirely reflected.
临界角取决于两种材料。对于玻璃到空气，临界角约为42°。当入射角大于临界角时，就没有光线折射出去——全部被反射。
12. Absorption, Transmission and Reflection of Waves – Summary | 波的吸收、透射与反射 – 总结
When a wave encounters a barrier or a new medium, three things can happen: absorption (wave energy is taken in by the material, often heating it up), transmission (the wave passes through), and reflection (the wave bounces back).
当波遇到障碍物或新介质时，可能发生三种情况：吸收（波的能量被材料吸收，通常使其升温）、透射（波通过）和反射（波被弹回）。
All three processes follow the law of conservation of energy: the total energy arriving equals the sum of absorbed, transmitted, and reflected energy. For example, a dark, matt surface absorbs most of the light falling on it (heating it), while a shiny surface reflects most light.
这三种过程都遵循能量守恒定律：到达的总能量等于被吸收、透射和反射的能量之和。例如，深色哑光表面吸收大部分照射到它上面的光（从而升温），而光亮的表面反射大部分光。
Understanding these interactions is vital for designing efficient solar panels, noise barriers, optical instruments, and safety equipment such as microwave oven shielding.
理解这些相互作用对于设计高效的太阳能电池板、隔音屏障、光学仪器以及微波炉屏蔽等安全设备至关重要。
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