IGCSE Edexcel Science: Light Revision Notes | IGCSE Edexcel 科学：光 考点精讲

📚 IGCSE Edexcel Science: Light Revision Notes | IGCSE Edexcel 科学：光 考点精讲

Light is a form of energy that travels in straight lines and is fundamental to the IGCSE Edexcel Science syllabus. Understanding its behaviour – reflection, refraction, lenses, and the electromagnetic spectrum – is key to mastering the physics of light. This revision guide covers all essential concepts, formulas, and practical skills needed for the exam.

光是一种沿直线传播的能量形式，是 IGCSE Edexcel 科学考纲的基础内容。掌握光的反射、折射、透镜及电磁波谱等行为，是攻克光学物理的关键。本复习指南涵盖考试所需的所有核心概念、公式和实验技能。

1. Properties of Light | 光的性质

Light travels in straight lines in a uniform medium. Its speed in a vacuum is approximately 3.0 × 10⁸ m/s. When light hits an opaque object, a shadow forms with a sharp umbra and a blurry penumbra if the source is extended. Light can be reflected, refracted, and dispersed.

光在均匀介质中沿直线传播，真空中的光速约为 3.0 × 10⁸ m/s。当光照射到不透明物体时，如果光源是扩展光源，会形成边缘清晰的暗本影和模糊的半影。光可以被反射、折射和色散。

Luminous objects emit their own light (e.g. the Sun, a lamp), while non-luminous objects are seen when they reflect light. We see an object because light enters the eye.

发光体能自己发光（如太阳、灯泡），非发光体靠反射光被看见。我们看到物体是因为光线进入了眼睛。

2. Reflection of Light | 光的反射

When light hits a smooth surface, it obeys the law of reflection: the angle of incidence i equals the angle of reflection r (measured from the normal), and the incident ray, reflected ray and normal all lie in the same plane.

当光照射到光滑表面时遵循反射定律：入射角 i 等于反射角 r（都从法线量起），入射光线、反射光线和法线在同一平面内。

A plane mirror forms a virtual image that is upright, laterally inverted, same size as the object, and located as far behind the mirror as the object is in front. Virtual images cannot be projected onto a screen because the light rays only appear to come from them.

平面镜形成正立、左右颠倒、与物体等大且位于镜后等距处的虚像。虚像不能被投射到屏幕上，因为光线只是看起来从虚像发出。

3. Refraction of Light | 光的折射

Refraction is the bending of light when it passes from one transparent medium to another due to a change in speed. When light enters a denser medium (e.g. from air to glass), it slows down and bends towards the normal. When 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介质时因速度变化而发生的弯曲。光进入光密介质（如从空气到玻璃）时速度变慢、向法线偏折；进入光疏介质时速度变快、偏离法线。

The angle of refraction r is the angle between the refracted ray and the normal. If the light enters along the normal, it passes straight through without bending.

折射角 r 是折射光线与法线的夹角。如果光线沿着法线入射，则直线通过不发生偏折。

4. Refractive Index and Snell’s Law | 折射率与斯涅尔定律

The refractive index n of a material is a measure of how much it slows down light. For light travelling from a vacuum (or air) into a material, n = sin i / sin r. This is Snell’s law. A higher refractive index means a greater bending effect.

介质的折射率 n 衡量其对光的减速程度。光从真空（或空气）进入某种材料时，n = sin i / sin r，这就是斯涅尔定律。折射率越高，弯曲效应越强。

n = sin i / sin r

For example, the refractive index of glass is about 1.5. You can find n by measuring angles i and r with a ray box and semi-circular glass block, then plotting a graph of sin i against sin r – the gradient gives n.

例如玻璃的折射率约为 1.5。可用光箱和半圆形玻璃块测量角度 i 和 r，然后绘制 sin i

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