GCSE Edexcel Science: Light – Key Revision Notes | GCSE Edexcel 科学：光

📚 GCSE Edexcel Science: Light – Key Revision Notes | GCSE Edexcel 科学：光 – 考点精讲

Light is a form of energy that travels in straight lines and allows us to see the world. In Edexcel GCSE Science, this topic covers how light behaves when it reflects, refracts, disperses, and interacts with lenses and colours. Understanding these principles is essential for tackling both calculation and explanation questions in your exam.

光是沿直线传播的能量形式，让我们得以看见世界。在 Edexcel GCSE 科学中，这一主题涵盖光的反射、折射、色散、与透镜和颜色的相互作用。掌握这些原理对于解决考试中的计算和解释题目至关重要。

1. The Nature of Light | 光的本质

Light is a transverse electromagnetic wave that does not need a medium to travel. In a vacuum, its speed is approximately 3.0 × 10⁸ m/s. Visible light is just a small part of the electromagnetic spectrum, lying between ultraviolet and infrared radiation.

光是横波，属于电磁波，无需介质即可传播。在真空中，光速约为 3.0 × 10⁸ 米/秒。可见光只是电磁波谱中的一小部分，位于紫外线和红外线之间。

We can model light using rays – straight lines with arrows showing the direction of travel. A beam of light may be parallel, converging or diverging. Shadows are formed when an opaque object blocks the path of light, producing areas of umbra (full shadow) and penumbra (partial shadow).

我们可以用光线来模型化光——带有箭头的直线表示传播方向。光束可以是平行的、会聚的或发散的。当不透明物体挡住光线时就会形成影子，产生本影（完全黑暗）和半影（部分黑暗）区域。

2. Reflection | 光的反射

When light hits a surface, it can be reflected. The law of reflection states that the angle of incidence (i) equals the angle of reflection (r), both measured from the normal – an imaginary line perpendicular to the surface.

当光射到表面时，会发生反射。反射定律指出入射角 (i) 等于反射角 (r)，两者均从法线（垂直于表面的假想线）量起。

Angle of incidence = Angle of reflection

Smooth surfaces produce specular (mirror-like) reflection where a clear image is formed. Rough surfaces cause diffuse reflection, where light is scattered in many directions and no image is seen. Both types still obey the law of reflection at each point on the surface.

光滑表面产生镜面反射，形成清晰图像。粗糙表面引起漫反射，光线向各个方向散射，看不见像。两种反射在表面每一点都仍然遵守反射定律。

3. Images in Plane Mirrors | 平面镜成像

A plane mirror forms an image that is virtual, upright, laterally inverted (left–right reversed), and the same size as the object. The image appears to be the same distance behind the mirror as the object is in front of it.

平面镜所成的像是虚像、正立、左右颠倒，且与物体大小相同。像看起来在镜后，与物体到镜面的距离相等。

Virtual images cannot be projected onto a screen because the light rays only appear to come from the image location – they do not actually converge there. You can locate such an image using the method of no parallax or by ray diagram construction.

虚像不能投影到屏幕上，因为光线只是看起来从像的位置发出——它们并未实际会聚。你可以通过无视差法或光线图绘制来找到虚像的位置。

4. Refraction | 光的折射

Refraction is the bending of light as 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.

折射指光从一种透明介质进入另一种介质时因速度改变而发生弯曲。当光进入光密介质（如从空气到玻璃）时，速度减慢，偏向法线；进入光疏介质时，速度加快，偏离法线。

If the incident ray hits the boundary along the normal (angle of incidence = 0°), it passes straight through without bending. The amount of bending depends on the optical densities of the two materials and the angle of incidence.

如果入射光线沿法线射入界面（入射角 = 0°），将直接穿入而不发生偏折。偏折程度取决于两种材料的光学密度以及入射角的大小。

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

The refractive index (n) of a material measures how much it slows down light compared with a vacuum. Snell’s law links the angles of incidence and refraction to the refractive indices of the two media. For a boundary between medium 1 and medium 2, the equation is:

材料的折射率 (n) 衡量光在该材料中相对于真空的减慢程度。斯涅尔定律将入射角和折射角与两种介质的折射率联系起来。对于介质1和介质2的界面，方程为：

n₁ sin θ₁ = n₂ sin θ₂

Most GCSE calculations involve light entering a transparent block from air (n ≈ 1). In such cases, the equation simplifies to n = sin i / sin r, where i is the angle in air and r is the angle in the material. This allows you to find the refractive index of a glass or Perspex block from experiment.

大多数 GCSE 计算涉及光从空气（n ≈ 1）进入透明块体的情形，此时方程简化为 n = sin i / sin r，其中 i 为空气中的角度，r 为材料中的角度。借此可通过实验求得玻璃或有机玻璃的折射率。

6. Total Internal Reflection | 全内反射

Total internal reflection (TIR) occurs when light travels from a denser to a less dense medium at an angle of incidence greater than the critical angle (c). At the critical angle, the refracted ray skims along the boundary at 90° to the normal. When i > c, all light is reflected back into the denser medium.

全内反射发生在光从光密介质射向光疏介质且入射角大于临界角 (c) 时。在临界角，折射光线沿界面以 90° 掠出。当 i > c 时，所有光被反射回光密介质。

The critical angle is related to the refractive index by sin c = 1/n. TIR is used in optical fibres for high-speed data transmission and in prism periscopes and reflectors because it is highly efficient – almost no light is lost.

临界角与折射率的关系为 sin c = 1/n。全内反射用于光纤进行高速数据传输，也用于棱镜潜望镜和反射器，因其效率很高——几乎没有光损失。

7. Dispersion of Light | 光的色散

When white light passes through a triangular glass prism, it is split into a spectrum of colours – red, orange, yellow, green, blue, indigo and violet (ROYGBIV). This happens because each colour has a slightly different wavelength and therefore a slightly different refractive index. Violet light is refracted the most; red light is refracted the least.

当白光通过三棱镜时，会被分解为一条彩色光谱——红、橙、黄、绿、蓝、靛、紫。这是因为每种颜色的波长略有不同，因而折射率也略有不同。紫光偏折最大，红光偏折最小。

This effect explains the formation of rainbows, where water droplets act as tiny prisms that both refract and internally reflect sunlight.

这一效应解释了彩虹的形成：小水滴充当了微小的棱镜，对阳光同时进行折射和内反射。

8. Colour and Filters | 颜色与滤光片

White light is made up of all the colours of the visible spectrum. The primary colours of light are red, green and blue – adding them together in different proportions produces all other colours, with red + green + blue giving white light. This is additive colour mixing.

白光由可见光谱中所有颜色组成。光的三原色是红、绿、蓝——将它们按不同比例叠加可产生所有其他颜色，红+绿+蓝得到白光。这称为加色混色。

A colour filter works by transmitting its own colour and absorbing the other colours. For example, a red filter transmits red light but absorbs green and blue. If you shine green light onto a red filter, almost no light passes through and the object appears black.

滤光片的作用是透射自身颜色并吸收其他颜色。例如，红色滤光片透射红光但吸收绿光和蓝光。如果让绿光照射红色滤光片，几乎没有光通过，物体呈黑色。

Coloured objects reflect certain wavelengths and absorb the rest. A red apple appears red because it reflects red light and absorbs the other colours. Under pure green light, it would appear black because there is no red light to reflect.

彩色物体反射特定波长并吸收其余。红苹果看起来是红色，因为它反射红光而吸收其他颜色。在纯绿光下，它会呈现黑色，因为没有红光可反射。

9. Lenses – Convex and Concave | 透镜——凸透镜与凹透镜

Lenses change the direction of light by refraction. A convex (converging) lens is thicker in the middle and brings parallel rays of light together at a focal point. The distance from the lens centre to the focal point is the focal length.

透镜通过折射改变光的方向。凸透镜（会聚透镜）中间厚，能使平行光线会聚到焦点上。透镜中心到焦点的距离称为焦距。

A convex lens can produce both real and virtual images depending on the object distance. If the object is beyond the focal point, a real, inverted image is formed on the opposite side. If the object is within the focal length, the image is virtual, upright and magnified – this is how a magnifying glass works.

凸透镜根据物距可产生实像或虚像。当物体在焦点之外，在对侧形成倒立实像；当物体在焦距之内，形成正立放大的虚像——这就是放大镜的原理。

A concave (diverging) lens is thinner in the middle and spreads parallel rays apart so they appear to diverge from a virtual focal point. Concave lenses always form virtual, upright and diminished images and are used to correct short-sightedness.

凹透镜（发散透镜）中间薄，使平行光线发散，看上去光线是从一个虚焦点发散出来的。凹透镜始终形成正立缩小虚像，常用于矫正近视。

10. Vision and Correction | 视觉与矫正

The eye uses a convex lens (the crystalline lens) to focus light onto the retina. The lens changes shape to focus on near and distant objects – a process called accommodation.

眼睛利用凸透镜（晶状体）将光线聚焦到视网膜上。晶状体改变形状以聚焦近处和远处的物体，这一过程称为调节。

Short sight (myopia) occurs when the eyeball is too long or the lens is too powerful, causing the image to focus in front of the retina. This is corrected with a diverging (concave) lens. Long sight (hyperopia) happens when the eyeball is too short or the lens is too weak, so the image focuses behind the retina; it is corrected using a converging (convex) lens.

近视（因眼球过长或晶状体过强）使像落在视网膜前方，用发散透镜（凹透镜）矫正。远视（因眼球过短或晶状体过弱）使像落在视网膜后方，用会聚透镜（凸透镜）矫正。

Both types of corrective lenses produce a clear virtual image at the person’s near point or far point so that the eye can then focus it sharply onto the retina.

两种矫正镜片都在人的近点或远点产生清晰虚像，使眼睛能将之清晰聚焦到视网膜上。

Published by TutorHao | GCSE Science Revision Series | aleveler.com

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GCSE Edexcel Science: Light – Key Revision Notes | GCSE Edexcel 科学：光 – 考点精讲