Electromagnetic Radiation | 电磁辐射

📚 Electromagnetic Radiation | 电磁辐射

Electromagnetic radiation is one of the most fundamental topics in CIE A-Level Physics. It describes how oscillating electric and magnetic fields carry energy through space, from radio waves used in communication to gamma rays emitted by radioactive nuclei. Understanding the electromagnetic spectrum, the wave equation c = fλ and the photon model E = hf is essential for both multiple-choice and structured questions, as well as for practical applications.

电磁辐射是 CIE A-Level 物理中最基础的主题之一。它描述振荡的电场和磁场如何在空间中携带能量，从通信所用的无线电波到放射性原子核发射的伽马射线。理解电磁波谱、波动方程 c = fλ 以及光子模型 E = hf 对选择题和结构化题目以及实际应用都至关重要。

1. The Nature of Electromagnetic Waves | 电磁波的本质

Electromagnetic waves are produced by accelerating charges. When a charged particle accelerates, it creates a changing electric field that generates a changing magnetic field; these fields sustain each other and propagate outward as a wave.

电磁波由加速电荷产生。当带电粒子加速时，它产生变化的电场，变化的电场又产生变化的磁场；这些场相互维持并以波的形式向外传播。

The electric field and magnetic field oscillate at right angles to each other and at right angles to the direction of energy transfer.

电场和磁场彼此垂直振荡，并且都与能量传递方向垂直。

Because no medium is required, electromagnetic waves can travel through a vacuum at a speed of about 3.00 × 10⁸ m s⁻¹.

由于不需要介质，电磁波可以在真空中以约 3.00 × 10⁸ m s⁻¹ 的速度传播。

2. Transverse Waves and Polarisation | 横波与偏振

All electromagnetic waves are transverse. This means the oscillations of the electric and magnetic fields are perpendicular to

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