📚 Reflection of Light | 光的反射
When you look in a mirror, light bounces off your face, hits the mirror and travels back to your eyes. This bouncing of light is called reflection. In this KS3 CIE article, you will learn how reflection works, the law that governs it, and why reflection is so important in everyday life.
当你照镜子时，光线从你的脸上反射到镜面，再进入你的眼睛。这种光的反弹现象就叫做反射。在这篇 KS3 CIE 文章中，你将学习反射的原理、支配反射的定律，以及反射在日常生活中为何如此重要。
1. What is Reflection? | 什么是反射？
Reflection happens when light rays strike a surface and bounce back. Light travels in straight lines, and when it meets a boundary between two materials, such as air and glass, some or all of the light can be sent back into the original material.
当光线照射到表面并反弹回来时，就会发生反射。光沿直线传播，当它遇到两种材料（例如空气和玻璃）之间的界面时，部分或全部光线会被送回原来的材料中。
Most objects do not produce their own light. We see them because light from a source, such as the Sun or a lamp, reflects off the object and enters our eyes.
大多数物体本身不发光。我们能看到它们，是因为来自太阳或灯等光源的光在物体表面发生反射，然后进入我们的眼睛。
In physics, reflection is studied using light rays, which are straight lines with arrows showing the direction the light travels.
在物理学中，我们使用光线来研究反射。光线是带箭头的直线，箭头表示光的传播方向。
2. Key Terms: Incident Ray, Reflected Ray and Normal | 关键术语：入射光线、反射光线与法线
To describe reflection accurately, we use three main terms. The incident ray is the incoming light ray that strikes the surface. The reflected ray is the light ray that bounces off the surface. The normal is an imaginary line drawn at a right angle (90°) to the surface at the point where the incident ray hits.
为了准确描述反射，我们使用三个主要术语。入射光线是照射到表面的入射光线。反射光线是从表面反弹回来的光线。法线是一条假想的线，在入射光线照射点处与表面成直角（90°）。
All angles in reflection are measured between the light ray and the normal, not between the light ray and the surface.
反射中的所有角度都是在光线与法线之间测量的，而不是在光线与表面之间测量的。
The point where the incident ray meets the surface is called the point of incidence.
入射光线与表面相交的点叫做入射点。
| Incident ray 入射光线 | The ray travelling towards the surface 射向表面的光线 |
| Reflected ray 反射光线 | The ray travelling away from the surface 离开表面的光线 |
| Normal 法线 | A dashed line at 90° to the surface 与表面成 90° 的虚线 |
| Angle of incidence 入射角 | Angle between incident ray and normal 入射光线与法线的夹角 |
| Angle of reflection 反射角 | Angle between reflected ray and normal 反射光线与法线的夹角 |
3. The Law of Reflection | 反射定律
The law of reflection states that the angle of incidence is always equal to the angle of reflection. This is true for all flat, smooth surfaces and for every single light ray.
反射定律指出，入射角始终等于反射角。这对所有平整光滑的表面以及每一条光线都成立。
We can write this law as:
我们可以把这个定律写成：
i = r
where i is the angle of incidence and r is the angle of reflection. Both angles are measured from the normal.
其中 i 是入射角，r 是反射角。两个角都从法线开始测量。
The incident ray, the reflected ray and the normal all lie in the same plane. This means you can draw all three on a flat piece of paper without any of them sticking out.
入射光线、反射光线和法线都在同一平面内。这意味着你可以在平坦的纸上画出这三者，而不会出现任何一条线突出纸面的情况。
The law of reflection applies to all types of waves, not just light. Sound waves and water waves also follow the same rule.
反射定律适用于所有类型的波，而不仅仅是光。声波和水波也遵循同样的规律。
4. Mirror Reflection vs Diffuse Reflection | 镜面反射与漫反射
When light hits a very smooth surface, such as a mirror or calm water, all reflected rays bounce off at the same angle. This produces a clear image and is called specular reflection, or mirror reflection.
当光照射到非常光滑的表面（如镜面或平静的水面）时，所有反射光线以相同的角度反弹。这会产生清晰的图像，称为镜面反射。
When light hits a rough surface, such as paper or a wall, the light rays are scattered in many different directions because the surface is uneven at a microscopic level. This is called diffuse reflection.
当光照射到粗糙表面（如纸或墙）时，光线会向许多不同的方向散射，因为表面在微观尺度上是不平的。这称为漫反射。
Diffuse reflection does not produce a clear image, but it allows us to see objects from any angle. That is why you can see a white wall from all parts of a room.
漫反射不会产生清晰的图像，但它使我们能够从任何角度看到物体。这就是你可以从房间的各个位置看到白墙的原因。
Both types of reflection obey the law of reflection for each individual ray. The difference is the direction of the normal on each tiny bump of the rough surface.
两种反射对每一条光线都遵循反射定律。区别在于粗糙表面每个微小凸起上的法线方向不同。
5. How to Draw a Reflection Diagram | 如何绘制反射光路图
Drawing a clear ray diagram helps you solve reflection problems. Start by drawing a straight horizontal line to represent the reflecting surface.
画一张清晰的光路图有助于解决反射问题。首先画一条水平直线来表示反射面。
Next, draw a dashed vertical line at the point where the incident ray will hit the surface. This is the normal. Label it with a small ‘N’ or the word normal.
接着，在入射光线将要射到表面的位置画一条垂直虚线。这就是法线。用小写字母 ‘N’ 或单词 normal 标注它。
Draw the incident ray coming from the top left towards the point of incidence, and the reflected ray bouncing away to the top right. Add arrowheads to show the direction of travel.
画出从左上方向入射点射来的入射光线，以及反弹到右上方的反射光线。添加箭头以显示传播方向。
Mark the angle of incidence i between the incident ray and the normal, and the angle of reflection r between the reflected ray and the normal. For a flat mirror, i and r should be equal.
标出入射角 i（入射光线与法线的夹角）和反射角 r（反射光线与法线的夹角）。对于平面镜，i 和 r 应该相等。
Always use a ruler and a sharp pencil. A common error is measuring the angle from the surface instead of from the normal.
始终使用直尺和削尖的铅笔。一个常见错误是从表面而不是从法线开始测量角度。
6. Plane Mirror Images | 平面镜成像
A plane mirror is a flat, smooth reflective surface. The image formed by a plane mirror has several important characteristics that you need to know for KS3 CIE.
平面镜是一个平坦光滑的反射面。平面镜所成的像有几个重要特征，这些是 KS3 CIE 需要掌握的。
The image is upright, the same size as the object, and laterally inverted. Lateral inversion means left and right are swapped in the image.
像是正立的，与物体大小相同，并且左右颠倒。左右颠倒意味着像中的左右互换了。
The image appears to be the same distance behind the mirror as the object is in front of the mirror. We say the image is virtual because the light rays do not actually pass through the image location.
像看起来在镜后，与物体在镜前的距离相等。我们说像是虚像，因为光线实际上并没有通过像的位置。
If you stand 2 m in front of a plane mirror, your image appears to be 2 m behind the mirror. The total distance between you and your image is 4 m.
如果你站在平面镜前 2 m 处，你的像看起来在镜后 2 m 处。你和你的像之间的总距离是 4 m。
Virtual images cannot be projected onto a screen. Real images can be projected, but plane mirrors always produce virtual images.
虚像不能投射到屏幕上。实像可以投射，但平面镜总是产生虚像。
7. Calculating Angles of Incidence and Reflection | 计算入射角和反射角
When solving reflection questions, first
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