KS3 CIE Revision of Light Answers | KS3 CIE 光复习答案

📚 KS3 CIE Revision of Light Answers | KS3 CIE 光复习答案

This revision guide gives clear, exam-style answers for the KS3 CIE topic of light. It covers how light travels, reflects, refracts, disperses, and how we see objects and colour. Use each section to check your understanding and correct common mistakes.

这份复习指南为 KS3 CIE 光学专题提供清晰的考试风格答案。它涵盖光的传播、反射、折射、色散，以及我们如何看到物体和颜色。使用每一节来检查你的理解并纠正常见错误。

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1. Light Travels in Straight Lines | 光沿直线传播

Light is a form of energy that travels in straight lines called rays. A ray is drawn as a straight arrow showing the direction of travel. A beam is made of many rays.

光是一种能量形式，沿直线传播，这些直线称为光线。光线用带箭头的直线表示，箭头指示传播方向。光束由许多光线组成。

We can see a light ray only when it enters the eye. In diagrams, always draw rays with a ruler and mark the direction with an arrow. The arrow must point from the light source towards the eye, not the other way.

只有当光线进入眼睛时，我们才能看到它。在示意图中，一定要用尺子画光线，并用箭头标出方向。箭头必须从光源指向眼睛，而不是相反。

Light travels at about 300,000,000 m/s in a vacuum. In air, its speed is almost the same. In water and glass, light travels more slowly, which helps explain refraction later.

光在真空中的速度约为 300,000,000 米/秒。在空气中速度几乎相同。在水中和玻璃中，光传播得更慢，这有助于解释后面的折射现象。

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2. Shadows, Eclipses and the Pinhole Camera | 影子、日食月食与针孔照相机

A shadow forms when an opaque object blocks light. Because light travels in straight lines, the shadow has a similar shape to the object. Translucent objects let some light through, so they make weak shadows. Transparent objects let almost all light through, so they do not form clear shadows.

当不透明物体阻挡光时，就会形成影子。因为光沿直线传播，影子的形状与物体相似。半透明物体让部分光通过，所以形成较淡的影子。透明物体几乎让所有光通过，因此不会形成清晰的影子。

An eclipse is a shadow in space. A solar eclipse happens when the Moon blocks sunlight from reaching part of the Earth. A lunar eclipse happens when the Earth blocks sunlight from reaching the Moon.

日食或月食是太空中的影子。日食发生在月球挡住太阳光，使其无法到达地球部分地区时。月食发生在地球挡住太阳光，使其无法到达月球时。

A pinhole camera uses a tiny hole to form an upside-down image on a screen. The image is real and inverted because light rays from the top of the object pass through the hole and end up at the bottom of the screen.

针孔照相机利用小孔在屏幕上形成倒立的像。像是实像且倒立，因为物体顶部的光线穿过小孔后到达屏幕底部。

If the pinhole is made smaller, the image becomes sharper but dimmer. If the screen is moved further from the pinhole, the image becomes larger but dimmer.

如果针孔变小，图像会变得更清晰但更暗。如果屏幕离针孔更远，图像会变大但更暗。

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3. Reflection from a Plane Mirror | 平面镜的反射

Reflection happens when light bounces off a surface. A plane mirror is a flat, smooth surface that reflects light regularly. This gives a clear image.

当光从表面反弹时，就发生了反射。平面镜是一个平整光滑的表面，能有规律地反射光，因此形成清晰的像。

The image in a plane mirror is upright, the same size as the object, and appears to be the same distance behind the mirror as the object is in front. The image is laterally inverted, which means left and right appear swapped.

平面镜中的像是正立的，与物体大小相同，并且看起来在镜后的距离与物体在镜前的距离相等。像是左右颠倒的，也就是左右看起来互换。

The image in a plane mirror is virtual. A virtual image cannot be projected onto a screen because the light rays do not actually pass through the image position; they only appear to come from behind the mirror.

平面镜中的像是虚像。虚像不能投射到屏幕上，因为光线实际上并没有通过像的位置；它们只是看起来从镜后发出。

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4. The Law of Reflection | 反射定律

The law of reflection states that the angle of incidence equals the angle of reflection. Both angles are measured from the normal, not from the mirror surface.

反射定律指出，入射角等于反射角。两个角都从法线测量，而不是从镜面测量。

The normal is an imaginary line drawn at 90 degrees to the surface at the point where the ray hits. The incident ray is the incoming ray, and the reflected ray is the outgoing ray.

法线是一条假想的线，在光线照射点处与表面成 90 度。入射光线是射入的光线，反射光线是射出的光线。

angle of incidence i = angle of reflection r

入射角 i = 反射角 r

For a ray hitting a plane mirror at 30 degrees to the mirror surface, the angle of incidence is not 30 degrees. Calculate it as 90 – 30 = 50 degrees. So the angle of reflection is also 50 degrees.

如果光线以与镜面成 30 度角射向平面镜，入射角不是 30 度。应计算为 90 – 30 = 50 度。因此反射角也是 50 度。

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5. Refraction: Light Bending at Boundaries | 折射：光在界面处的弯曲

Refraction is the change in direction of light when it passes from one transparent material to another, such as from air into glass or water. It happens because light changes speed.

折射是光从一种透明材料进入另一种透明材料时方向的改变，例如从空气进入玻璃或水中。它发生的原因是光的速度发生了改变。

When light enters a denser medium like glass from air, it slows down and bends towards the normal. When light leaves the denser medium and enters air, it speeds up and bends away from the normal.

当光从空气进入玻璃等更密的介质时，速度减慢并向法线方向偏折。当光离开较密介质进入空气时，速度加快并偏离法线方向。

If a ray hits the boundary exactly along the normal, it passes straight through without bending. The angle of incidence is 0 degrees, so the angle of refraction is also 0 degrees.

如果光线正好沿法线射入界面，它会直直穿过而不发生偏折。入射角为 0 度，因此折射角也为 0 度。

A common example is a straw in a glass of water. The straw looks bent or broken at the water surface because light from the underwater part changes direction when it leaves the water and enters the air.

一个常见的例子是水杯中的吸管。吸管在水面处看起来弯曲或折断，因为来自水下部分的光在离开水进入空气时改变了方向。

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6. Dispersion and the Visible Spectrum | 色散与可见光谱

White light is a mixture of different colours. When white light passes through a triangular glass prism, it splits into the colours of the visible spectrum. This splitting is called dispersion.

白光是不同颜色的混合体。当白光穿过三棱镜时，它会被分解成可见光谱的各种颜色。这种分解称为色散。

The colours of the visible spectrum in order are red, orange, yellow, green, blue, indigo and violet. A useful memory phrase is ‘Richard Of York Gave Battle In Vain’.

可见光谱的颜色顺序是红、橙、黄、绿、蓝、靛、紫。一个有用的记忆短语是 ‘Richard Of York Gave Battle In Vain’。

Dispersion happens because each colour has a slightly different speed inside glass. Red light slows down the least and is bent the least. Violet light slows down the most and is bent the most.

色散发生的原因是每种颜色在玻璃中的速度略有不同。红光减慢得最少，偏折也最少。紫光减慢得最多，偏折也最多。

A rainbow is an example of dispersion. Water droplets in the air act like tiny prisms, splitting sunlight into its colours.

彩虹是色散的一个例子。空气中的水滴像小棱镜一样，把太阳光分解成各种颜色。

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7. How We See Colour | 我们如何看到颜色

We see objects because light reflects off them and enters our eyes. The colour of an object depends on which colours of light it reflects and which colours it absorbs.

我们能看到物体，是因为光从物体反射并进入我们的眼睛。物体的颜色取决于它反射哪些颜色的光以及吸收哪些颜色的光。

A red apple looks red in white light because it reflects red light and absorbs the other colours. A white shirt looks white because it reflects all colours of the spectrum. A black object looks black because it absorbs nearly all colours and reflects very little.

一个红苹果在白光下看起来是红色，因为它反射红光并吸收其他颜色。白衬衫看起来是白色，因为它反射光谱中的所有颜色。黑色物体看起来是黑色，因为它几乎吸收所有颜色，反射很少的光。

Colour filters work by transmitting only some colours and absorbing others. A red filter lets red light through and absorbs other colours. If you shine pure green light through a red filter, almost no light passes, so the filter appears black.

彩色滤光片的工作原理是只透射某些颜色并吸收其他颜色。红色滤光片让红光通过并吸收其他颜色。如果用纯绿光照射红色滤光片，几乎没有光通过，因此滤光片看起来是黑色。

If an object is viewed in coloured light, its appearance can change. A blue object in red light looks black because there is no blue light to reflect. A white object in green light looks green because it reflects green light.

如果物体在彩色光下观察，它的外观可能会改变。蓝色物体在红光下看起来是黑色，因为没有蓝光可以反射。白色物体在绿光下看起来是绿色，因为它反射绿光。

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8. Lenses and the Human Eye | 透镜与人眼

A convex lens is thicker in the middle than at the edges. It converges light rays to a focus. The distance from the centre of the lens to the focus is called the focal length.

凸透镜中间比边缘厚。它使光线会聚到焦点。从透镜中心到焦点的距离称为焦距。

A convex lens can form real and inverted images on a screen. If the object is far away, the image is smaller. If the object is close but beyond the focus, the image can be larger and inverted.

凸透镜可以在屏幕上形成倒立的实像。如果物体较远，像较小。如果物体较近但在焦点之外，像可以更大且倒立。

The eye contains a convex lens that focuses light onto the retina. The retina is a light-sensitive layer at the back of the eye. The image on the retina is real, inverted and smaller than the object. The brain interprets this image as upright.

眼睛含有一个凸透镜，将光聚焦到视网膜上。视网膜是眼球后部的感光层。视网膜上的像是实像、倒立且比物体小。大脑将这个像解读为正立。

The iris controls how much light enters the eye through the pupil. In bright light, the pupil becomes smaller. In dim light, the pupil becomes larger. The cornea also helps focus light before it passes through the lens.

虹膜控制通过瞳孔进入眼睛的光量。在强光下，瞳孔变小。在弱光下，瞳孔变大。角膜在光通过晶状体之前也有助于聚焦光线。

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9. Key Measurements and Units | 关键测量与单位

When answering exam questions on light, always name the correct equipment and state the correct unit. Angles are measured in degrees using a protractor.

在回答光学考试题时，一定要写出正确的器材和单位。角度用量角器测量，单位是度。

To investigate reflection, place a plane mirror on a sheet of paper. Draw the incident ray, the normal and the reflected ray. Use a protractor to measure the angle between each ray and the normal. Repeat for different incident angles.

要研究反射，将平面镜放在一张纸上。画出入射光线、法线和反射光线。用量角器测量每条光线与法线之间的夹角。对不同的入射角重复实验。

For refraction, use a glass block or water tank. Shine a ray of light at the surface and mark the path of the ray before and after the block. Draw the normal at each boundary and measure the angles of incidence and refraction.

对于折射，使用玻璃块或水槽。将一束光照在表面上，并在玻璃块前后标出光线的路径。在每个界面处画出法线，测量入射角和折射角。

The speed of light is not usually measured in KS3 labs because it is extremely fast. Instead, you may be asked to recall its approximate value: 3 × 10⁸ m/s.

光速通常不在 KS3 实验室中测量，因为它极快。相反，你可能会被要求记住它的近似值：3 × 10⁸ m/s。

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10. Common Misconceptions and Exam Answers | 常见误区与考试答案

A very common mistake is to think that we see objects because the eye sends out rays. The correct idea is that light reflects from the object into the eye. Check your ray diagrams carefully: the arrow must point towards the eye.

一个非常常见的错误是认为我们看到物体是因为眼睛发出光线。正确的概念是光从物体反射进入眼睛。仔细检查你的光线图：箭头必须指向眼睛。

Another misconception is that shadows are always completely black. In fact, shadows can have a dark central region called the umbra and a lighter outer region called the penumbra when the light source is large.

另一个误区是影子总是完全黑色的。事实上，当光源较大时，影子可以有一个较暗的中心区域称为本影，和一个较亮的外部区域称为半影。

Students sometimes say that in a mirror the image swaps left and right completely. It is better to say the image is laterally inverted. The mirror does not swap top and bottom.

学生有时说镜子中的像完全左右互换。更好的说法是像是左右颠倒的。镜子不会上下颠倒。

For refraction, do not say ‘light bends because it hits the glass’. The correct explanation is that light bends because it changes speed when it enters a different medium. If asked about direction, say towards the normal when slowing down, and away from the normal when speeding up.

对于折射，不要说 ‘光弯曲是因为它碰到了玻璃’。正确的解释是光弯曲是因为它进入不同介质时速度发生了变化。如果被问及方向，要说明减速时向法线偏折，加速时偏离法线。

For colour, do not say ‘a red object absorbs red light’. That is backwards. A red object reflects red light and absorbs the other colours.

对于颜色，不要说 ‘红色物体吸收红光’。那是反的。红色物体反射红光并吸收其他颜色。

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11. Quick Practice Questions with Answers | 快速练习题与答案

Question 1: State the law of reflection.

问题 1：陈述反射定律。

Answer: The angle of incidence equals the angle of reflection, measured from the normal.

答案：入射角等于反射角，均从法线测量。

Question 2: A light ray hits a mirror. The angle between the incident ray and the mirror surface is 20 degrees. What is the angle of reflection?

问题 2：一束光照射到镜面。入射光线与镜面的夹角为 20 度。反射角是多少？

Answer: Angle of incidence = 90 – 20 = 70 degrees, so the angle of reflection is also 70 degrees.

答案：入射角 = 90 – 20 = 70 度，因此反射角也是 70 度。

Question 3: Why does a pencil look bent when placed in a glass of water?

问题 3：为什么铅笔放在水杯中看起来是弯的？

Answer: Light from the underwater part of the pencil refracts at the water-air surface. The rays change direction, so the pencil appears bent.

答案：来自铅笔水下部分的光在水与空气界面发生折射。光线改变方向，所以铅笔看起来弯曲。

Question 4: Name the colours of the visible spectrum in order.

问题 4：按顺序说出可见光谱的颜色。

Answer: Red, orange, yellow, green, blue, indigo, violet.

答案：红、橙、黄、绿、蓝、靛、紫。

Question 5: A blue object is viewed in red light. What colour does it appear? Explain.

问题 5：蓝色物体在红光下观察。它看起来是什么颜色？请解释。

Answer: It appears black because it can only reflect blue light. Red light contains no blue light, so the object reflects almost nothing.

答案：它看起来是黑色，因为它只能反射蓝光。红光不含蓝光，所以物体几乎不反射任何光。

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12. Summary Checklist | 复习清单

• Light travels in straight lines and can be shown by rays with arrows.

  光沿直线传播，可以用带箭头的光线表示。

• Shadows, eclipses and pinhole camera images are explained by straight-line propagation.

  影子、日食月食和针孔照相机成像都可以用直线传播来解释。

• The law of reflection: angle of incidence equals angle of reflection, measured from the normal.

  反射定律：入射角等于反射角，从法线测量。

• Refraction is the bending of light due to a change in speed between media.

  折射是光由于在不同介质中速度改变而发生的弯曲。

• White light disperses into red, orange, yellow, green, blue, indigo and violet.

  白光色散为红、橙、黄、绿、蓝、靛、紫。

• Colour appearance depends on which wavelengths are reflected or transmitted.

  颜色外观取决于哪些波长的光被反射或透射。

• A convex lens focuses light; the eye uses a convex lens to form an inverted image on the retina.

  凸透镜会聚光线；眼睛利用凸透镜在视网膜上形成倒像。

• Always draw the normal and measure angles from it in reflection and refraction diagrams.

  在反射和折射图中，一定要画出法线并从法线测量角度。

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