📚 Light Waves – IGCSE Edexcel Physics | 光波 – IGCSE Edexcel 物理
Light waves form a core part of the IGCSE Edexcel Physics syllabus, covering geometric optics, electromagnetic waves, and practical applications. A solid understanding of reflection, refraction, total internal reflection, dispersion, and lens behaviour is essential for both examination success and for appreciating how optical technology shapes our world.
光波是IGCSE Edexcel物理课程的核心，涵盖几何光学、电磁波和实际应用。透彻掌握反射、折射、全内反射、色散和透镜行为，对考试成功和理解光学技术如何塑造世界至关重要。
1. What Are Light Waves? | 什么是光波？
rection of energy transfer. In a vacuum all electromagnetic waves travel at 3.0 × 10⁸ m/s.
光是一种不需要介质传播的电磁波，以横波形式传播，电场和磁场互相垂直且垂直于能量传递方向。在真空中所有电磁波的速度均为3.0 × 10⁸ 米/秒。
Unlike mechanical waves such as sound, light can travel through a vacuum. Its wave nature is demonstrated by interference and diffraction, but at IGCSE level the focus is on geometric optics, using rays to describe how light behaves at boundaries and through lenses.
与声波等机械波不同，光可以在真空中传播。光的波动性通过干涉和衍射展现，但IGCSE阶段重点是利用光线描述光在界面和透镜中的行为，即几何光学。
2. The Electromagnetic Spectrum | 电磁波谱
Visible light is a very small slice of the electromagnetic spectrum. The full spectrum, in order of increasing frequency (and decreasing wavelength), is: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. All these waves are transverse and travel at the same speed in a vacuum.
可见光只是电磁波谱中极小的一部分。整个波谱按频率递增（波长递减）的顺序为：无线电波、微波、红外线、可见光、紫外线、X射线和伽马射线。这些波都是横波，在真空中速度相同。
The visible spectrum ranges from red (longest wavelength, ~700 nm) to violet (shortest wavelength, ~400 nm). The colour sequence can be recalled as ROYGBIV: red, orange, yellow, green, blue, indigo, violet. Each band of the EM spectrum has practical uses: microwaves for cooking, infrared for remote controls and thermal imaging, ultraviolet for sterilisation, X-rays for medical scans, and gamma rays for cancer therapy.
可见光谱从红光（波长最长，约700纳米）到紫光（约400纳米），颜色顺序可按ROYGBIV记忆：红、橙、黄、绿、蓝、靛、紫。电磁波谱各波段具有实际用途：微波烹饪、红外遥控与热成像、紫外线消毒、X射线医学检查和伽马射线癌症治疗。
3. Reflection of Light | 光的反射
The law of reflection states that the angle of incidence equals the angle of reflection, with both angles measured from the normal – an imaginary line perpendicular to the surface at the point of incidence. The incident ray, reflected ray and normal all lie in the same plane.
反射定律指出，入射角等于反射角，两个角度都从法线（入射点处垂直于表面的假想线）开始测量。入射光线、反射光线和法线位于同一平面内。
On a smooth surface, specular reflection produces a clear image. On a rough surface, diffuse reflection scatters light in many directions; even so, the law of reflection holds at each microscopic point. A plane mirror forms a virtual, upright, laterally inverted image that is the same size as the object and appears to be as far behind the mirror as the object is in front.
光滑表面发生镜面反射，产生清晰图像；粗糙表面发生漫反射，光朝各个方向散射，但每一微观点仍遵循反射定律。平面镜形成虚像、正立、左右颠倒，像与物等大，且像距镜后等于物距镜前。
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. This occurs because light changes speed at the boundary. When entering a denser medium (e.g. air to glass), light slows down and bends towards the normal. When entering 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的弯曲。这是因为光在界面处速度改变。进入光密介质（如空气到玻璃）时速度减慢，向法线靠拢；进入光疏介质时速度加快，偏离法线。
The amount of bending depends on the refractive indices of the two materials. A wavefront diagram explains why the direction changes: one side of the wavefront reaches the new medium first and changes speed, causing the whole wave to pivot.
弯曲程度取决于两种材料的折射率。波前图能解释方向变化的原因：波前的一侧先进入新介质并改变速度，导致整束波发生偏转。
5. Refractive Index and Snell's Law | 折射率与斯涅尔定律
r has n ≈ 1.00. The greater the refractive index, the more the light slows down and bends.
介质的绝对折射率n是光在真空中的速度c与在介质中的速度v之比：n = c / v，为无量纲数，且始终 ≥ 1。空气的n ≈ 1.00。折射率越大，光减速越多，弯曲越明显。
Snell' he angle of incidence in air and r is the angle of refraction in the second medium, and n is the refractive index of that medium.
斯涅尔定律关联角度与折射率：n₁ sin θ₁ = n₂ sin θ₂。若第一种介质是空气（n₁ ≈ 1），则简化为 n = sin i / sin r，其中 i 是空气中的入射角，r 是第二种介质中的折射角，n 是该介质的折射率。
n = sin i / sin r
This formula is used to calculate unknown angles or refractive indices from experimental data.
此公式用于根据实验数据计算未知角度或折射率。
6. Total Internal Reflection and Critical Angle | 全内反射与临界角
Total internal reflection (TIR) occurs when light travels from a denser medium to a less dense medium and the angle of incidence is greater than the critical angle c. At the critical angle, the angle of refraction is 90°; the refracted ray runs along the boundary. For incidence angles beyond c, all light is reflected back into the denser medium.
当光从光密介质射向光疏介质，且入射角大于临界角c时，发生全内反射（TIR）。在临界角下，折射角为90°，折射光线沿界面传播。超过临界角时
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