📚 OCR Science: Waves Revision Guide | OCR 科学：波 考点精讲
Waves are a fundamental topic in OCR GCSE Science, carrying energy and information all around us, from sound and light to earthquakes. This guide covers everything you need to know for the exam — wave types, key properties, the wave equation, reflection, refraction, the electromagnetic spectrum, and required practicals — with clear explanations and exam tips.
波是 OCR GCSE 科学中的一个基础主题，能量和信息通过声波、光波、地震波等在我们周围传递。本指南涵盖考试所需的所有知识点——波的类型、关键性质、波速方程、反射、折射、电磁波谱以及必做实验——配有清晰的解释和考试技巧。
1. Types of Waves | 波的种类
Waves transfer energy from one place to another without transferring matter. | 波将能量从一个地方传递到另一个地方而不传递物质。
Mechanical waves need a medium (solid, liquid or gas) to travel through, while electromagnetic waves do not require a medium and can travel through a vacuum. | 机械波需要介质（固体、液体或气体）才能传播，而电磁波不需要介质，可以在真空中传播。
Examples of mechanical waves include sound waves, water waves and seismic waves. | 机械波的例子包括声波、水波和地震波。
All electromagnetic waves are transverse and travel at the speed of light in a vacuum. | 所有电磁波都是横波，在真空中以光速传播。
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. | 在横波中，振动方向与能量传递方向垂直（成直角）。
Light, water waves and all electromagnetic waves are transverse. | 光、水波以及所有电磁波都是横波。
Transverse waves have crests (peaks) and troughs. | 横波有波峰和波谷。
In a longitudinal wave, the vibrations are parallel to the direction of energy transfer. | 在纵波中，振动方向与能量传递方向平行。
Sound waves and P-type seismic waves are longitudinal. | 声波和 P 型地震波是纵波。
Longitudinal waves consist of compressions (regions of high pressure) and rarefactions (regions of low pressure). | 纵波由压缩区（高压区域）和稀疏区（低压区域）组成。
Remember the key exam point: Transverse = perpendicular; Longitudinal = parallel. | 请记住考试关键点：横波 = 垂直；纵波 = 平行。
3. Wave Properties: Amplitude, Wavelength, Frequency, Period | 波的性质：振幅、波长、频率、周期
The amplitude of a wave is the maximum displacement from the equilibrium position. | 振幅是波从平衡位置的最大位移。
In a transverse wave, amplitude is the height of a crest or depth of a trough from the middle line. | 在横波中，振幅是波峰或波谷到中间线的高度。
Greater amplitude means more energy carried by the wave. | 振幅越大意味着波携带的能量越多。
The wavelength (λ) is the distance between two identical points on consecutive waves, e.g. crest to crest or compression to compression. | 波长 (λ) 是相邻波上两个相同点之间的距离，例如波峰到波峰或压缩区到压缩区。
The frequency (f) is the number of complete waves passing a point per second, measured in hertz (Hz). | 频率 (f) 是每秒通过某点的完整波的个数，单位是赫兹 (Hz)。
ime taken for one complete wave to pass a point, and it is linked to frequency by T = 1/f. | 周期 (T) 是一个完整波通过某点所需的时间，它与频率的关系为 T = 1/f。
All these properties can be determined from a wave diagram or oscilloscope trace. | 所有这些性质都可以从波形图或示波器轨迹中确定。
4. The Wave Equation | 波速方程
The wave speed (v), frequency (f) and wavelength (λ) are related by the wave equation: | 波速 (v)、频率 (f) 和波长 (λ) 由波速方程关联：
v = f × λ
Wave speed is measured in metres per second (m/s), frequency in hertz (Hz) and wavelength in metres (m). | 波速的单位是米每秒 (m/s)，频率的单位是赫兹 (Hz)，波长的单位是米 (m)。
To solve problems, rearrange the equation as needed: f = v / λ or λ = v / f. | 解题时可根据需要移项：f = v / λ 或 λ = v / f。
Always convert units to SI before substituting numbers — wavelength is often given in cm or mm. | 代入数字前一定要将单位转换为国际单位制——波长常常以 cm 或 mm 给出。
For electromagnetic waves in a vacuum, v is the speed of light c = 3.0 × 10⁸ m/s. | 对于真空中的电磁波，v 等于光速 c = 3.0 × 10⁸ m/s。
The wave equation also applies to sound waves, water waves and seismic waves, provided the correct speed is used. | 波速方程也适用于声波、水波和地震波，只要使用正确的波速。
5. Reflection of Waves | 波的反射
Reflection occurs when a wave bounces off a surface. | 反射发生在波从表面反弹时。
The law of reflection states that the angle of incidence equals the angle of reflection, measured from the normal. | 反射定律指出，入射角等于反射角，角度从法线量起。
Smooth, flat surfaces produce clear reflections (specular reflection), while rough surfaces scatter waves in many directions (diffuse reflection). | 光滑平整的表面产生清晰的反射（镜面反射），而粗糙表面会使波向多个方向散射（漫反射）。
Echoes are examples of sound wave reflection; sonar uses reflected ultrasound to map the seafloor. | 回声是声波反射的例子；声纳利用反射的超声波绘制海床地图。
Wavefront diagrams help visualise reflection: the incoming wavefronts are parallel, and the reflected wavefronts also remain parallel but change direction. | 波前图有助于理解反射：入射波前平行，反射波前也保持平行但改变了方向。
6. Refraction of Waves | 波的折射
Refraction is the change in direction of a wave when it passes from one medium to another at an angle, due to a change in speed. | 折射是波以一定角度从一种介质进入另一种介质时，因速度变化而导致的方向改变。
The frequency of the wave stays the same during refraction, but the wavelength and speed change. | 折射过程中波的频率保持不变，但波长和速度发生变化。
When a wave enters a denser medium (e.g. light entering glass from air), it slows down and bends towards the normal. | 当波进入更密的介质时（例如光从空气进入玻璃），波速减慢并向法线偏折。
When a wave enters a less dense medium (e.g. light exiting glass into air), it speeds up and bends away from the normal. | 当波进入较疏介质时（例如光从玻璃进入空气），波速加快并偏离法线。
Water waves refract when moving from deep water to shallow water: they slow down and the wavelength decreases, causing the wavefronts to bend. | 水波从深水区进入浅水区时会折射：波速减慢，波长减小，导致波前弯曲。
7. Sound Waves | 声波
Sound waves are longitudinal waves caused by vibrating objects. | 声波是由物体振动产生的纵波。
They need a medium to travel; sound cannot travel through a vacuum. | 声波需要介质传播；声音不能在真空中传播。
The speed of sound in air is approximately 330 m/s, but it travels faster in solids and liquids because particles are closer together. | 声音在空气中的速度约为 330 m/s，但在固体和液体中传播更快，因为粒子间距更小。
The human ear can detect sound frequencies from about 20 Hz to 20,000 Hz (20 kHz). | 人耳可探测的声音频率范围约为 20 Hz 至 20,000 Hz (20 kHz)。
Sound below 20 Hz is called infrasound, and sound above 20 kHz is ultrasound. | 频率低于 20 Hz 的声音称为次声波，高于 20 kHz 的称为超声波。
Ultrasound is used in medical imaging, cleaning delicate items, and measuring distances (e.g. sonar). | 超声波用于医学成像、精密物件清洗以及距离测量（例如声纳）。
Loudness is related to amplitude, and pitch is related to frequency. | 响度与振幅有关，音调与频率有关。
8. The Electromagnetic Spectrum | 电磁波谱
The electromagnetic spectrum is a continuous range of transverse waves that all travel at the speed of light in a vacuum. | 电磁波谱是一系列连续的横波，它们在真空中均以光速传播。
The spectrum is ordered by wavelength (or frequency), and from longest wavelength to shortest the main groups are: | 该波谱按照波长（或频率）排序，从长波到短波的主要类别为：
Radio waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma rays. | 无线电波、微波、红外线、可见光、紫外线、X 射线、伽马射线。
A helpful mnemonic is ‘Raging Martians Invaded Venus Using X-ray Guns’. | 一个助记口诀是 ‘Raging Martians Invaded Venus Using X-ray Guns’。
As wavelength decreases, frequency and energy increase. | 波长递减时，频率和能量递增。
All electromagnetic waves can be reflected, refracted and transmitted. | 所有电磁波都可被反射、折射和透射。
Visible light is the only part of the spectrum detectable by human eyes; it ranges from red (longest wavelength) to violet (shortest wavelength). | 可见光是电磁波谱中仅有人眼可探测的部分，范围从红光（最长波长）到紫光（最短波长）。
9. Uses and Dangers of EM Waves | 电磁波的用途与危害
Radio waves: used for broadcasting and communications; no known danger at typical exposure levels. | 无线电波：用于广播和通信；通常暴露水平下无已知危害。
Microwaves: used for cooking (microwave ovens) and satellite communications; can cause internal heating of body tissue. | 微波：用于烹饪（微波炉）和卫星通信；可能引起人体组织内部加热。
Infrared: used for thermal imaging, remote controls and heating; intense exposure can cause skin burns. | 红外线：用于热成像、遥控器及加热；强烈暴露可导致皮肤灼伤。
Visible light: used for seeing, photography and fibre optic communications; too bright light can damage the retina. | 可见光：用于视觉、摄影和光纤通信；过强的光线会损伤视网膜。
Ultraviolet (UV): used in fluorescent lamps and sterilisation; overexposure causes sunburn, skin ageing and increases the risk of skin cancer. | 紫外线 (UV)：用于荧光灯和消毒；过度暴露会导致晒伤、皮肤老化并增加皮肤癌风险。
X-rays: used for medical imaging and security scanning; they are ionising and can cause mutations or cancer. | X 射线：用于医学成像和安检扫描；具有电离性，可导致突变或癌症。
Gamma rays: used to sterilise medical equipment and treat cancer; high energy and strongly ionising, causing serious cell damage. | 伽马射线：用于医疗设备灭菌和癌症治疗；高能且强电离，造成严重细胞损伤。
Ionising radiation (UV, X-rays, gamma) can knock electrons out of atoms; limit exposure with shielding and distance. | 电离辐射（紫外线、X 射线、伽马射线）能将电子从原子中击出；应通过屏蔽和距离限制暴露。
10. Seismic Waves and Earth Structure | 地震波与地球结构
Earthquakes produce seismic waves: P-waves (primary) are longitudinal and travel through solids and liquids. | 地震产生地震波：P 波（初波）是纵波，能穿过固体和液体。
S-waves (secondary) are transverse and travel only through solids. | S 波（次波）是横波，只能在固体中传播。
By studying how P-waves and S-waves travel through Earth, scientists have inferred that the outer core is liquid because S-waves cannot pass through it. | 通过研究 P 波和 S 波在地球内部的传播方式，科学家推断外核是液态的，因为 S 波无法通过外核。
Seismic wave speeds change at boundaries between layers, providing evidence for Earth’s internal structure (crust, mantle, outer core, inner core). | 地层层间边界处地震波速度会改变，这为地球内部结构（地壳、地幔、外核、内核）提供了证据。
This is a common exam question linking waves to geology. | 这是考试中常见的将波与地质学相联系的问题。
11. Measuring Wave Speed (Required Practical) | 测量波速（必做实验）
Water waves in a ripple tank: Set up a ripple tank with a light source above and a screen below. Use a vibrating bar to generate waves at a known frequency. | 用涟漪槽测量水波：搭建涟漪槽，上方设光源、下方设屏幕。用振动条以已知频率产生波。
wave pattern or using a ruler placed on the screen; calculate wave speed using v = f × λ. | 通过拍摄波形图或在屏幕上使用尺子测量波长；用方程 v = f × λ 计算波速。
e for a wave crest to travel a measured distance directly and use speed = distance / time. | 此外，也可直接测量一个波峰移动一段给定距离的时间，用速度 = 距离 / 时间 计算。
Sound waves: To measure the speed of sound, stand a large distance away from a wall, make a sharp sound and measure the time taken for the echo to return. | 声波：测量声速时，站在离墙壁很远的地方，发出一个尖锐的声音并测量回声返回所需的时间。
Use speed = 2 × distance / time (because sound travels to the wall and back). | 使用公式 速度 = 2 × 距离 / 时间（因为声音往返传播）。
erages to improve accuracy; keep the frequency constant when using v = fλ to avoid errors. | 重复实验取平均值以提高准确性；使用 v = fλ 时保持频率恒定以避免误差。
12. Exam Tips and Common Mistakes | 考试技巧与常见错误
Always state that waves transfer energy, not matter. | 一定要说明波传递的是能量，而不是物质。
Use the terms "compression" and "rarefaction" for longitudinal waves; use "crest" and "trough" for transverse. | 对纵波使用 "压缩" 和 "稀疏" 术语；对横波使用 "波峰" 和 "波谷"。
Check units: convert kHz to Hz (×1000), cm to m (÷100) before using the wave equation. | 检查单位：在使用波速方程前，将 kHz 换算成 Hz（×1000）、cm 换算成 m（÷100）。
When explaining refraction, mention change in speed leading to change in direction; frequency remains unchanged. | 解释折射时，要提及速度变化导致方向改变；频率保持不变。
For EM spectrum questions, know the order and be able to match each wave to a use and a danger. | 在电磁波谱题目中，要记住顺序并能将每种波与一项用途和一项危害对应。
ces, the horizontal scale gives time (period), allowing frequency calculation via f = 1/T. | 在示波器轨迹上，水平轴表示时间（周期），可用 f = 1/T 计算频率。
In ray diagrams for reflection, add the normal (dotted line) and mark equal angles with arcs; label incident ray and reflected ray. | 在反射光线图中，添加法线（虚线）并用弧线标记等角；标注入射光线和反射光线。
Do not confuse amplitude with wavelength: amplitude is from the middle line to a crest, wavelength is crest to next crest. | 不要混淆振幅和波长：振幅是从中间线到波峰，波长是波峰到下一个波峰。
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