📚 GCSE Edexcel Science: Waves Key Points Revision | GCSE Edexcel 科学：波 考点精讲
Waves transfer energy without transferring matter. Mastering the properties and behaviours of waves is crucial for success in the GCSE Edexcel Science specification. This revision guide covers transverse and longitudinal waves, key equations, reflection, refraction, diffraction, sound, the electromagnetic spectrum, seismic waves, and practical skills.
波在不传递物质的情况下传递能量。掌握波的性质和行为对 GCSE Edexcel 科学考试至关重要。本考点精讲涵盖横波与纵波、核心方程、反射、折射、衍射、声波、电磁波谱、地震波以及实验技能。
1. Types of Waves: Transverse and Longitudinal | 波的类型：横波与纵波
In a transverse wave, the oscillations are perpendicular to the direction of energy transfer. The wave has crests and troughs. Examples include ripples on a water surface, waves on a rope, and all electromagnetic waves.
在横波中，振动方向与能量传递方向垂直。波包含波峰和波谷。例如水面涟漪、绳波以及所有电磁波都是横波。
In a longitudinal wave, the oscillations are parallel to the direction of energy transfer. They are made up of compressions (regions of high pressure) and rarefactions (regions of low pressure). Sound waves in air and seismic P-waves are longitudinal.
在纵波中，振动方向与能量传递方向平行。纵波由密部（高压区）和疏部（低压区）组成。空气中的声波和地震P波是纵波。
2. Describing Waves: Wavelength, Frequency, Amplitude and Period | 描述波的物理量：波长、频率、振幅和周期
Wavelength (λ) is the distance between two consecutive identical points on a wave, such as crest to crest or compression to compression. It is measured in metres (m). Frequency (f) is the number of complete wave cycles passing a point per second, measured in hertz (Hz). Amplitude is the maximum displacement from the rest position – in a transverse wave it is the height of a crest from equilibrium; in a longitudinal wave it relates to the maximum pressure in a compression.
波长（λ）是两个相邻相同点之间的距离，例如波峰到波峰或密部到密部，单位是米（m）。频率（f）是每秒通过某点的完整波数，单位是赫兹（Hz）。振幅是离开平衡位置的最大位移——在横波中是波峰距平衡位置的高度；在纵波中与密部的最大压力有关。
Period (T) is the time taken for one complete wave cycle. It is the reciprocal of frequency: T = 1/f. If the frequency is 50 Hz, the period is 0.02 s.
周期（T）是完成一次完整振动所需的时间，是频率的倒数：T = 1/f。若频率为 50 Hz，周期为 0.02 s。
3. The Wave Equation: v = f × λ | 波速方程：v = f × λ
Wave speed (v), frequency (f) and wavelength (λ) are linked by the equation v = f × λ. Speed is measured in metres per second (m/s). This is one of the most important equations on the GCSE specification. You must be able to use it and rearrange it to find f = v / λ or λ = v / f.
波速（v）、频率（f）和波长（λ）的关系为 v = f × λ。波速的单位是米每秒（m/s）。这是 GCSE 考纲中最重要的方程之一。你必须能够运用该式，并变形求出 f = v / λ 或 λ = v / f。
Example: A water wave has a frequency of 5 Hz and a wavelength of 0.8 m. Its speed is v = 5 × 0.8 = 4 m/s. If a sound wave travels at 330 m/s and has a wavelength of 1.5 m, its frequency is f = 330 / 1.5 = 220 Hz.
示例：一水波频率为 5 Hz，波长为 0.8 m，波速 v = 5 × 0.8 = 4 m/s。一声波波速 330 m/s，波长 1.5 m，频率 f = 330 / 1.5 = 220 Hz。
4. Reflection of Waves | 波的反射
When waves hit a boundary between two different media, they can be reflected. The angle of incidence equals the angle of reflection, both measured relative to a line called the normal (a line perpendicular to the surface). This applies to light, sound (echoes) and water waves.
波遇到两种不同介质边界时会反射。入射角等于反射角，两者均相对于法线（垂直于表面的直线）测量。这适用于光、声（回声）和水波。
In a ripple tank, straight water waves hitting a flat barrier are reflected and change direction. Sound waves reflect from hard, smooth surfaces to produce echoes; ultrasound reflection is used in sonar to detect objects and measure distances underwater.
在水波槽中，平直水波碰到平板屏障会反射并改变方向。声波从坚硬光滑表面反射产生回声；超声波反射用于声纳探测水下物体并测量距离。
5. Refraction of Waves | 波的折射
Refraction happens when waves cross a boundary into a different medium and their speed changes. Unless the wave hits along the normal, this change in speed causes the wave to change direction. For light waves, entering a denser medium (like glass) slows the wave down, bending it towards the normal. When sound waves travel into warmer air, they speed up and bend away from the normal.
折射发生在波穿过边界进入不同介质并改变速度时。除非波正好沿法线入射，速度的改变会导致波改变方向。对于光波，进入光密介质（如玻璃）时速度变慢，向法线偏折。声波进入更热的空气时速度加快，偏离法线偏折。
Crucially, the frequency of the wave remains constant during refraction because it is determined by the source. Using v = f × λ, if speed decreases, wavelength must also decrease. This is a common exam point.
关键的一点是，折射过程中波的频率保持不变，因为频率由波源决定。由 v = f × λ 可知，速度减小时波长必定减小。这是常见的考点。
6. Diffraction of Waves | 波的衍射
Diffraction is the spreading out of waves when they pass through a gap or travel around an obstacle. The effect is most significant when the gap size is comparable to the wavelength. If the gap is much larger than the wavelength, diffraction is minimal. This explains why we can hear sound around a corner (sound wavelengths are about 0.1–1 m) but light does not visibly bend around the same corner (light wavelengths are around 400–700 nm).
衍射是波通过缝隙或绕过障碍物时扩散的现象。当缝隙尺寸与波长相当时，衍射效果最显著。如果缝隙远大于波长，衍射微小。这解释了为何我们能听到拐角处的声音（声波波长约为 0.1–1 m），而光不能绕同个拐角明显弯曲（光波长约为 400–700 nm）。
Diffraction is a property of all waves. In a ripple tank, using a narrow gap produces a circular wavefront, demonstrating clear diffraction.
衍射是所有波的特性。在水波槽实验中，使用窄缝会产生圆形波前，清晰展示衍射。
7. Sound Waves | 声波
Sound waves are longitudinal waves caused by vibrating objects. They require a medium (solid, liquid or gas) to travel; they cannot travel through a vacuum. The speed of sound is approximately 330 m/s in air, around 1500 m/s in water, and up to 5000 m/s in steel. As a rule, sound travels faster in solids than in liquids, and faster in liquids than in gases.
声波是由振动引起的纵波，需要介质（固体、液体或气体）传播，不能在真空中传播。声速在空气中约 330 m/s，在水中约 1500 m/s，在钢中可达 5000 m/s。总的来说，声波在固体中比在液体中快，在液体中比在气体中快。
The human hearing range is approximately 20 Hz to 20,000 Hz. Frequencies above 20,000 Hz are called ultrasound. Ultrasound has many important applications: medical scanning (e.g. prenatal imaging), sonar for depth measurement, and industrial testing to detect cracks in metals.
人耳听觉范围约为 20 Hz 到 20,000 Hz。高于 20,000 Hz 的频率称为超声波。超声波有许多重要应用：医学扫描（如产前影像）、用于测深的声纳、以及工业上探测金属裂纹的探伤。
8. The Electromagnetic Spectrum | 电磁波谱
Electromagnetic (EM) waves are transverse waves that all travel at the same speed in a vacuum: 3.0 × 10⁸ m/s. The spectrum groups waves by wavelength and frequency. In order of decreasing wavelength (and increasing frequency), the seven main types are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
电磁波是横波，在真空中传播速度均相同，为 3.0 × 10⁸ m/s。电磁波谱按波长和频率划分。按波长递减（频率递增）的顺序，七种主要类型为：无线电波、微波、红外线、可见光、紫外线、X 射线和伽马射线。
The table below summarises key regions, wavelengths, uses and hazards. (Wavelength ranges are approximate.)
下表总结了主要波段、波长、用途和危害（波长范围为近似值）。
| Region / 波段 | Approximate wavelength / 近似波长 | Uses / 用途 | Hazards / 危害 |
|---|---|---|---|
| Radio waves 无线电波 | > 0.1 m | Broadcasting, communications | Generally low; no ionising effect |
| Microwaves 微波 | 0.1 m – 1 mm | Satellite signals, mobile phones, cooking | Internal heating of body tissue |
| Infrared 红外线 | 1 mm – 700 nm | Thermal imaging, remote controls, heaters | Skin burns |
| Visible light 可见光 | 700 nm – 400 nm | Vision, photography, optical fibres | Bright light can damage the retina |
| Ultraviolet 紫外线 | 400 nm – 10 nm | Sunbeds, fluorescent lamps, sterilisation | Sunburn, skin cancer, eye damage |
| X-rays X 射线 | 10 nm – 0.01 nm | Medical imaging, airport security | Cell damage, cancer, mutations |
| Gamma rays 伽马射线 | < 0.01 nm | Sterilising equipment, cancer radiotherapy | Severe cell damage, cancer, mutations |
All electromagnetic waves transfer energy and can be absorbed, reflected or transmitted. The higher the frequency, the more energy the wave carries. Gamma rays are the most penetrating and ionising.
所有电磁波都能传递能量，并可以被吸收、反射或透射。频率越高，波携带的能量越多。伽马射线的穿透力和电离能力最强。
9. Uses and Dangers of EM Waves in Detail | 电磁波的应用与危害详解
Radio waves are used for television and radio broadcasting because they can travel long distances and diffract around obstacles. Microwaves are used in satellite communications as they can pass through the ionosphere; in ovens they heat food by making water molecules vibrate. Their hazard
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