📚 IGCSE CCEA Science: Light – Key Revision Points | IGCSE CCEA 科学：光 考点精讲
This revision guide covers the essential topics on light for the CCEA IGCSE Science specification. By understanding the behaviour of light, including reflection, refraction, total internal reflection, lenses, and dispersion, you will be well prepared for your exam. We break down each concept with clear explanations in both English and Chinese.
本复习指南涵盖了 CCEA IGCSE 科学大纲中有关光的关键主题。通过理解光的特性，包括反射、折射、全内反射、透镜和色散，你将为考试做好充分准备。我们用中英文双语清晰解释每个概念。
1. Properties of Light | 光的性质
Light is a form of electromagnetic radiation that travels in straight lines. This rectilinear propagation explains how shadows are formed. When light strikes an opaque object, a sharp shadow is cast because light cannot bend around corners.
光是一种沿直线传播的电磁辐射。这种直线传播的性质解释了影子是如何形成的。当光照射到不透明物体上时，会形成清晰的影子，因为光不能绕过角落。
oted as c). In other transparent media, such as water or glass, light travels more slowly.
真空中的光速大约为 3.0 × 10⁸ m/s（通常用 c 表示）。在其他透明介质（如水或玻璃）中，光的传播速度较慢。
2. Reflection of Light | 光的反射
Reflection occurs when light bounces off a surface. The law of reflection states that: the angle of incidence (i) equals the angle of reflection (r), and the incident ray, reflected ray, and the normal all lie in the same plane.
反射是指光从表面弹回的现象。反射定律指出：入射角 (i) 等于反射角 (r)，且入射线、反射线和法线都在同一平面内。
∠i = ∠r
Smooth surfaces produce specular (regular) reflection, where parallel incident rays remain parallel after reflection (e.g., mirrors). Rough surfaces cause diffuse reflection, scattering light in many directions (e.g., paper).
光滑表面产生镜面（规则）反射，平行的入射光线反射后仍保持平行（如镜子）。粗糙表面则引起漫反射，将光线散射到各个方向（如纸张）。
3. Plane Mirrors | 平面镜
A plane mirror forms an image that is upright, laterally inverted (left and right are swapped), the same size as the object, and virtual (cannot be cast onto a screen). The image distance behind the mirror is equal to the object distance in front of it.
平面镜所成的像是正立、左右颠倒、与物体等大的虚像（无法投影到屏幕上）。像在镜后的距离等于物在镜前的距离。
In ray diagrams, we use dashed lines for virtual rays behind the mirror and solid lines for real rays in front.
在光路图中，我们用虚线表示镜后的虚光线，实线表示镜前的实光线。
4. Refraction of Light | 光的折射
Refraction is the bending of light when it passes from one transparent medium to another of different optical density. If light enters a denser medium (e.g., from air to glass), it slows down and bends towards the normal. If it enters a less dense medium, it speeds up and bends away from the normal.
折射是光从一种透明介质进入另一种光密度不同的介质时发生弯曲的现象。如果光进入密度较大的介质（如从空气到玻璃），速度减慢并靠近法线偏折。如果进入密度较小的介质，速度加快并远离法线偏折。
Snell's law relates the angles and refractive indices:
斯涅尔定律将角度和折射率联系起来：
