📚 IGCSE WJEC Science: Waves Revision | IGCSE WJEC 科学：波 考点精讲
Waves are a fundamental concept in physics, transferring energy from one place to another without transferring matter. In the IGCSE WJEC Science specification, you need to understand wave types, properties, behaviours such as reflection, refraction and diffraction, and applications including sound and the electromagnetic spectrum. This comprehensive revision guide covers all the essential points with paired English–Chinese explanations to strengthen your understanding for the exam.
波是物理学中的一个基本概念，它把能量从一个地方传递到另一个地方，而不会传递物质。在 IGCSE WJEC 科学考试大纲中，你需要理解波的类型、性质、反射、折射和衍射等行为，以及包括声音和电磁波谱在内的应用。这份全面的考点精讲以英中对照的方式覆盖所有要点，帮助你在考试中加深理解。
1. What is a Wave? | 什么是波？
A wave is a disturbance that carries energy through a medium or through empty space, without any net movement of the particles of the medium. Waves are produced by vibrations or oscillations. For example, a pebble dropped into water creates ripples that travel outwards, but the water itself does not travel with the wave.
波是一种扰动，它通过介质或真空传递能量，而介质粒子不发生净位移。波是由振动或振荡产生的。例如，投入水中的石子会产生向外扩散的涟漪，但水本身并不随波移动。
There are two main types of mechanical waves: transverse and longitudinal. The distinction depends on the direction of particle oscillation relative to the direction of energy transfer.
机械波主要有两种类型：横波和纵波。区别取决于粒子振动的方向与能量传播方向的关系。
2. Types of Waves: Transverse and Longitudinal | 波的类型：横波与纵波
In a transverse wave, the particles of the medium oscillate perpendicular (at right angles) to the direction of energy transfer. Examples include waves on a string, water ripples, and all electromagnetic waves. The crest is the highest point and the trough is the lowest point.
在横波中，介质粒子的振动方向与能量传递方向垂直（成直角）。例子包括绳波、水波涟漪以及所有电磁波。波峰是最高点，波谷是最低点。
In a longitudinal wave, the particles oscillate parallel to the direction of energy transfer, creating compressions (regions of high pressure) and rarefactions (regions of low pressure). Sound waves and seismic P-waves are longitudinal waves.
在纵波中，粒子振动方向与能量传递方向平行，形成压缩区（高压区）和稀疏区（低压区）。声波和地震 P 波是纵波。
You must be able to identify and sketch the two types, labelling key features such as wavelength, amplitude, and points of compression/rarefaction.
你必须能够识别并画出两种波的示意图，标出波长、振幅、压缩/稀疏点等关键特征。
3. Wave Properties: Amplitude, Wavelength, Frequency, Period | 波的性质：振幅、波长、频率、周期
Amplitude (A) is the maximum displacement of a point on the wave from its rest position. It is related to the energy carried by the wave: larger amplitude means more energy.
振幅 (A) 是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：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 or compression to compression. It is measured in metres (m).
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中心到压缩中心。单位是米 (m)。
Frequency (f) is the number of complete waves passing a fixed point per second. It is measured in hertz (Hz), where 1 Hz = 1 wave per second.
频率 (f) 是每秒通过固定点的完整波的数量。单位是赫兹 (Hz)，1 Hz 表示每秒一个波。
The period (T) is the time taken for one complete wave to pass a point. It is inversely related to frequency: T = 1/f. The period is measured in seconds (s).
周期 (T) 是一个完整波通过某点所需的时间。它与频率成反比：T = 1/f。周期的单位是秒 (s)。
4. The Wave Equation | 波动方程
The speed of a wave (v) can be calculated from its frequency and wavelength using the wave equation. This relationship applies to all types of waves.
波速 (v) 可以通过频率和波长使用波动方程计算。这一关系适用于所有类型的波。
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). You should be able to rearrange the equation to find any of the three quantities.
其中 v 是波速，单位为米/秒 (m/s)；f 是频率，单位为赫兹 (Hz)；λ 是波长，单位为米 (m)。你需要能够变换该方程求出任意一个量。
When waves travel from one medium to another, their speed and wavelength change, but their frequency stays the same. This is crucial for understanding refraction.
当波从一种介质进入另一种介质时，波速和波长发生变化，但频率保持不变。这对理解折射至关重要。
5. Reflection of Waves | 波的反射
Reflection occurs when a wave bounces back after hitting a surface. The law of reflection states that the angle of incidence (θi) equals the angle of reflection (θr), measured relative to the normal (a line perpendicular to the surface).
反射发生时，波在碰到表面后反弹回来。反射定律指出，入射角 (θi) 等于反射角 (θr)，两者都从法线（垂直于表面的线）量起。
In a ripple tank, you can observe straight water waves reflecting from a flat barrier. The reflected wave fronts maintain the same wavelength and frequency as the incident waves.
在波纹槽中，可以观察到平面水波从平直障碍物上反射。反射波前的波长和频率与入射波相同。
Reflection is used in many applications, including mirrors, echoes, and sonar. For sound waves, echoes are produced when sound reflects off a hard surface.
反射在许多应用中都有使用，包括镜子、回声和声纳。对于声波，当声音从坚硬表面反射时就会产生回声。
6. Refraction of Waves | 波的折射
Refraction is the change in direction of a wave when it passes from one medium into another with a different density, due to a change in speed. If the wave slows down, it bends towards the normal; if it speeds up, it bends away from the normal.
折射是波从一种介质进入另一种不同密度的介质时，由于速度变化而发生的方向改变。如果波减速，它会向法线偏折；如果波加速，它会远离法线偏折。
In a ripple tank, water waves slow down when they enter shallower water, causing their wavelength to decrease and the waves to bend. The frequency remains unchanged, so the wave equation v = fλ explains why wavelength changes with speed.
在波纹槽中，水波进入浅水区时会减速，导致波长减小并发生弯曲。频率不变，因此波动方程 v = fλ 解释了为什么波长随速度变化。
Refraction of light is seen when a straw appears bent in a glass of water. For sound, temperature changes in the air can cause refraction, which is why sounds can travel further at night.
光的折射可以观察到，比如吸管在水中看起来是弯折的。对于声音，空气中温度变化会引起折射，这就是声音在夜间能传播更远的原因。
7. Diffraction of Waves | 波的衍射
Diffraction is the spreading out of waves when they pass through a gap or around an obstacle. The amount of diffraction depends on the size of the gap compared to the wavelength: significant diffraction occurs when the gap width is approximately equal to or smaller than the wavelength.
衍射是波通过缝隙或绕过障碍物时发生扩散的现象。衍射的程度取决于缝隙大小与波长的比较：当缝隙宽度近似等于或小于波长时，衍射最为明显。
If the gap is much wider than the wavelength, the waves pass through with little spreading. You should be able to interpret diagrams showing wave fronts spreading into the shadow region.
如果缝隙远大于波长，波通过时几乎不扩散。你需要能够解释展现波前扩散到阴影区域的示意图。
Diffraction explains why you can hear sounds around corners but cannot see around them: sound waves have longer wavelengths comparable to doorways, whereas light wavelengths are extremely small.
衍射解释了为什么你可以听到拐角处的声音却无法看到它们：声波的波长较长，与门洞尺寸相当，而光波波长极小。
8. Sound Waves | 声波
Sound waves are longitudinal mechanical waves, meaning they require a medium (solid, liquid, or gas) to travel. They are produced by vibrating sources and travel as a series of compressions and rarefactions.
声波是纵机械波，这意味着它们需要介质（固体、液体或气体）才能传播。它们由振动源产生，并以一系列压缩和稀疏的形式传播。
The speed of sound varies in different media: fastest in solids, slower in liquids, and slowest in gases. In air at room temperature, sound travels at approximately 340 m/s. Sound cannot travel through a vacuum.
声音在不同介质中的速度不同：固体中最快，液体中较慢，气体中最慢。在室温空气中，声速大约为 340 m/s。声音不能在真空中传播。
The human ear detects sound when the vibrating air particles cause the eardrum to vibrate. The frequency of the sound wave determines the pitch; higher frequency gives a higher pitch. Amplitude relates to loudness.
当振动的空气粒子使鼓膜振动时，人耳便感知到声音。声波的频率决定音调；频率越高，音调越高。振幅与响度有关。
Ultrasound is sound with frequencies above 20 000 Hz, beyond human hearing. It has many uses, including medical imaging, sonar, and cleaning delicate equipment.
超声波是频率超过 20000 Hz 的声音，超出人类听觉范围。它有许多用途，包括医学成像、声纳和精密设备清洗。
9. Electromagnetic Waves | 电磁波
Electromagnetic (EM) waves are transverse waves that can travel through a vacuum. They all travel at the same speed in a vacuum: 3.0 × 10⁸ m/s, known as the speed of light. They do not require a medium.
电磁波是可以在真空中传播的横波。它们在真空中的速度相同：3.0 × 10⁸ m/s，即光速。它们不需要介质。
The electromagnetic spectrum is a continuous family of waves ordered by frequency and wavelength. From longest wavelength to shortest, the main groups are: Radio waves, Microwaves, Infrared, Visible light, Ultraviolet (UV), X-rays, Gamma rays.
电磁波谱是按频率和波长排列的连续波族。从长波长到短波长，主要类群为：无线电波、微波、红外线、可见光、紫外线、X 射线、伽马射线。
Different EM waves have different properties and uses. Radio waves are used for communication; microwaves for cooking and satellite transmissions; infrared for thermal imaging and remote controls; visible light allows us to see; UV causes sun tanning and can sterilise; X-rays are used in medical imaging; gamma rays are used to treat cancer and in sterilisation.
不同的电磁波有不同的性质和用途。无线电波用于通信；微波用于烹饪和卫星传输；红外线用于热成像和遥控器；可见光让我们看见；紫外线导致晒黑并可杀菌；X 射线用于医学影像；伽马射线用于癌症治疗和杀菌。
You need to recall the order of the spectrum and be able to compare the wavelengths and frequencies of different regions. Remember: as frequency increases, wavelength decreases, and the energy carried by the wave increases. Gamma rays have the highest frequency and therefore the highest energy.
你需要记住频谱的顺序，并能够比较不同区域的波长和频率。记住：频率增加，波长减小，波携带的能量增加。伽马射线频率最高，因此能量也最高。
10. Seismic Waves and Earthquakes | 地震波与地震
WJEC Science often includes seismic waves. Earthquakes produce two main types of seismic waves: P-waves (primary waves) and S-waves (secondary waves). P-waves are longitudinal and travel faster, arriving first at detection stations. S-waves are transverse and slower, arriving second.
WJEC 科学通常包括地震波。地震产生两种主要地震波：P 波（初至波）和 S 波（次至波）。P 波是纵波，传播较快，最先到达检测站。S 波是横波，较慢，后到达。
P-waves can travel through both solids and liquids, while S-waves can only travel through solids. This property provides evidence for the liquid outer core of the Earth, because S-waves are not detected on the side opposite an earthquake.
P 波能穿过固体和液体，而 S 波只能穿过固体。这一特性为地球外核呈液态提供了证据，因为在地震的对跖点检测不到 S 波。
The study of seismic waves helps scientists understand the Earth’s internal structure and is an important application of wave behaviour.
地震波研究帮助科学家了解地球内部结构，是波动行为的一个重要应用。
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