IGCSE WJEC Physics: Waves Key Points | IGCSE WJEC 物理：波 考点精讲

📚 IGCSE WJEC Physics: Waves Key Points | IGCSE WJEC 物理：波 考点精讲

Waves are one of the most exciting topics in IGCSE Physics, connecting everyday phenomena from music to earthquakes. This guide covers everything you need for WJEC, with clear explanations of wave properties, behaviours, and the electromagnetic spectrum.

波是IGCSE物理中最令人兴奋的主题之一，它将音乐到地震等日常现象联系起来。本指南涵盖了WJEC考试所需的一切，清晰地解释了波的性质、行为以及电磁波谱。

1. Wave Basics | 波的基础

A wave is a disturbance that transfers energy from one place to another without transferring matter. The key parameters are amplitude (maximum displacement from rest position), wavelength (λ, distance between two successive crests), frequency (f, number of waves per second, measured in hertz, Hz), and period (T, time for one complete wave, T = 1/f).

波是一种将能量从一个地方传递到另一个地方的扰动，而不传递物质。关键参数有振幅（离开平衡位置的最大位移）、波长（λ，两个相邻波峰之间的距离）、频率（f，每秒波的个数，单位赫兹Hz）和周期（T，完成一个完整波的时间，T=1/f）。

• Amplitude relates to the energy carried by a wave: larger amplitude means more energy.
• 振幅与波携带的能量有关：振幅越大，能量越多。
• Wavelength λ is measured in metres (m).
• 波长λ以米（m）为单位。

2. Transverse and Longitudinal Waves | 横波与纵波

In transverse waves, the oscillations are perpendicular to the direction of energy transfer. Examples include light, all electromagnetic waves, water ripples, and S-waves from earthquakes. In longitudinal waves, the oscillations are parallel to the direction of energy transfer. Sound waves, ultrasound, and P-waves from earthquakes are longitudinal.

在横波中，振动方向与能量传递方向垂直。例如光、所有电磁波、水波纹和地震中的S波。在纵波中，振动方向与能量传递方向平行。声波、超声波和地震中的P波是纵波。

• Transverse waves show crests and troughs; longitudinal waves show compressions and rarefactions.
• 横波有波峰和波谷；纵波有压缩和稀疏区域。
• You should be able to label amplitude, wavelength, compression, and rarefaction on diagrams.
• 你应能够在图上标出振幅、波长、压缩和稀疏。

3. Wave Equation | 波速方程

The wave speed (v) is related to frequency and wavelength by the equation:

波速（v）与频率和波长之间的关系由以下方程给出：

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). You must be able to rearrange this equation, for example λ = v / f.

其中v是以米/秒（m/s）为单位的波速，f是以赫兹（Hz）为单位的频率，λ是以米（m）为单位的波长。你必须能够对该方程进行变形，例如λ = v / f。

• All electromagnetic waves travel at the same speed in a vacuum, c = 3.0 × 10⁸ m/s.
• 所有电磁波在真空中的速度相同，c = 3.0 × 10⁸ m/s。
• Sound travels at about 340 m/s in air, faster in solids and liquids.
• 声音在空气中的速度约为340 m/s，在固体和液体中更快。

4. Reflection of Waves | 波的反射

Reflection occurs when a wave bounces off a surface. The law of reflection states that the angle of incidence (i) equals the angle of reflection (r), measured from the normal (a line perpendicular to the surface). This applies to all waves, including light and sound.

当波从表面弹回时发生反射。反射定律指出：入射角（i）等于反射角（r），两者都从法线（垂直于表面的线）量起。这适用于所有波，包括光和声。

• Reflection can produce echoes and is used in sonar and medical ultrasound imaging.
• 反射可以产生回声，并用于声纳和医学超声成像。
• When drawing ray diagrams, use a ruler, label the normal, and show arrows.
• 画光线图时，使用直尺，标出法线，并画出箭头。

5. Refraction of Waves | 波的折射

Refraction is the change in direction of a wave as it passes from one medium to another due to a change in speed. For light, when entering a denser medium (e.g., air to glass), the wave slows down and bends towards the normal. If it speeds up, it bends away from the normal.

折射是由于波速变化，波从一种介质进入另一种介质时方向发生改变的现象。对于光来说，当进入更密的介质时（如从空气到玻璃），波速减慢并向法线弯曲。如果波速增加，则远离法线弯曲。

• Water waves refract when they move from deep to shallow water: wavelength decreases, speed decreases, and they bend towards the normal (if entering at an angle).
• 水波从深水区运动到浅水区时发生折射：波长减小，速度减小，并向法线弯曲（如果斜向进入的话）。
• Frequency remains constant during refraction; only speed and wavelength change.
• 折射过程中频率保持不变；只有速度和波长改变。

6. Diffraction | 衍射

Diffraction is the spreading out of waves when they pass through a gap or around an obstacle. The effect is most noticeable when the gap width or obstacle size is comparable to the wavelength. Diffraction is a key property of all waves.

衍射是波通过缝隙或绕过障碍物时发生扩散的现象。当缝隙宽度或障碍物尺寸与波长相当时，衍射效应最为明显。衍射是所有波的一个关键特性。

• For a fixed wavelength, a narrower gap produces more spreading. For a fixed gap, a longer wavelength diffracts more.
• 对于固定波长，缝隙越窄，扩散越明显。对于固定缝隙，波长越长，衍射越强。
• Radio waves (long wavelength) diffract around hills, which is why you can receive radio signals even when the transmitter is not in sight.
• 无线电波（长波长）可以绕过山丘，这就是为什么即使看不到发射塔也能接收无线电信号。

7. Sound Waves | 声波

Sound waves are longitudinal waves caused by vibrating objects. They require a medium (solid, liquid, or gas) to travel and cannot pass through a vacuum. The speed of sound varies: about 340 m/s in air, 1500 m/s in water, and up to 5000 m/s in steel.

声波是由物体振动引起的纵波。它们需要介质（固体、液体或气体）才能传播，不能在真空中传播。声速因介质而异：空气中约为340 m/s，水中约为1500 m/s，钢中可高达5000 m/s。

• Human hearing range is roughly 20 Hz to 20 000 Hz. Frequencies above this are called ultrasound.
• 人耳的听觉范围大约为20 Hz到20 000 Hz。高于这一范围的频率称为超声波。
• Ultrasound is used in medical scanning (prenatal checks) and industrial testing (detecting cracks).
• 超声波用于医学扫描（产前检查）和工业检测（探测裂缝）。

8. Electromagnetic Spectrum | 电磁波谱

Electromagnetic (EM) waves are transverse waves that travel at 3.0 × 10⁸ m/s in a vacuum. The EM spectrum is arranged by wavelength or frequency, from long-wavelength radio waves to short-wavelength gamma rays. The main groups in order of increasing frequency (decreasing wavelength) are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.

电磁波是横波，在真空中以3.0 × 10⁸ m/s的速度传播。电磁波谱按波长或频率排列，从长波长的无线电波到短波长的伽马射线。按频率递增（波长递减）的顺序，主要分为：无线电波、微波、红外线、可见光、紫外线、X射线、伽马射线。

You must know the uses and dangers of each:

你必须了解每一种电磁波的用途和危害：

EM Wave / 电磁波	Uses / 用途	Dangers / 危害
Radio waves	Broadcasting, communications	None at normal levels
Microwaves	Cooking, satellite transmissions	Internal heating of body tissue
Infrared	Thermal imaging, remote controls	Skin burns
Visible light	Seeing, optical fibres	Eye damage from bright light
Ultraviolet	Sterilisation, detecting forged bank notes	Sunburn, skin cancer
X-rays	Medical imaging, security scanners	Cell damage, cancer
Gamma rays	Cancer treatment, sterilising equipment	Cell mutation, cancer

All EM waves travel at the same speed in a vacuum. Higher frequency means shorter wavelength and more energy.

所有电磁波在真空中速度相同。频率越高，波长越短，能量越大。

9. Seismic Waves | 地震波

Seismic waves are produced by earthquakes. There are two main types of body waves: P-waves (primary) are longitudinal and travel through solids and liquids; they are faster. S-waves (secondary) are transverse and can only travel through solids; they are slower. Surface waves (L-waves) travel along the Earth’s surface and cause most damage.

地震波由地震产生。主要有两种体波：P波（纵波）是纵波，能穿过固体和液体，速度较快。S波（横波）是横波，只能穿过固体，速度较慢。面波（L波）沿地球表面传播，造成大部分破坏。

• The study of S-wave shadow zones provides evidence that the Earth’s outer core is liquid, because S-waves cannot pass through it.
• 研究S波阴影区为地外核是液态提供了证据，因为S波无法穿过它。

10. Wave Behaviour and Communication | 波的行为与通信

Waves are vital for communication. Radio waves are used for TV and radio; microwaves for mobile phones and Wi-Fi; infrared for short-range devices. Optical fibres use total internal reflection of visible or infrared light to carry data with high speed and low loss.

波对通信至关重要。无线电波用于电视和广播；微波用于手机和Wi-Fi；红外线用于短距离设备。光纤利用可见光或红外线的全反射来高速、低损耗地传输数据。

• Digital signals are less prone to interference than analogue signals and can carry more information.
• 数字信号比模拟信号更不易受干扰，且能携带更多信息。
• Satellite communication uses microwaves that pass through the ionosphere.
• 卫星通信使用能穿过电离层的微波。

11. Key Experiments and Skills | 关键实验与技能

WJEC expects you to interpret oscilloscope traces for sound waves, measure the speed of water ripples using a ripple tank, and investigate refraction using a glass block. You should be able to describe how to measure the speed of sound in air using an echo method (timing the delay between clap and echo over a known distance).

WJEC期望你能解读声波的示波器波形，使用水波槽测量水波纹的速度，以及使用玻璃块研究折射。你应能描述如何利用回声法测量空气中的声速（记录拍手与回声之间的时间延迟，已知距离）。

• Speed = distance / time. For a standing wave on a string, measure the length of one loop to find half a wavelength.
• 速度 = 距离/时间。对于绳上的驻波，测量一个波环的长度即为半个波长。

12. Summary and Exam Tips | 总结与应试技巧

Remember: v=fλ is central. Know the difference between transverse and longitudinal by the direction of oscillation. For the EM spectrum, memorise the order and at least one use and danger per type. Practice ray diagrams for reflection and refraction. Use correct units and significant figures. In longer questions, link wave properties to everyday applications.

记住：v=fλ是核心。根据振动方向区分横波和纵波。对于电磁波谱，记住顺序以及每种波的至少一个用途和危害。练习反射和折射的光线图。使用正确的单位和有效数字。在长答题中，将波的性质与日常生活应用联系起来。

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