IB Science: Light – Key Concepts and Exam Tips | IB 科学：光 考点精讲

📚 IB Science: Light – Key Concepts and Exam Tips | IB 科学：光 考点精讲

Light is one of the most fascinating topics in the IB Science curriculum, bridging the gap between classical optics and modern wave theory. From the simple law of reflection to the complex interference patterns that reveal light’s wave nature, a strong understanding of these concepts is essential for success in both Standard Level and Higher Level examinations. This article breaks down the key principles, equations, and problem-solving strategies you need to master.

光是 IB 科学课程中最引人入胜的主题之一，它连接了经典光学与现代波动理论。从简单的反射定律到揭示光波动本性的复杂干涉图样，透彻理解这些概念是 Standard Level 和 Higher Level 考试成功的关键。本文梳理了你需要掌握的核心原理、方程和解题策略。

1. The Dual Nature of Light | 光的波粒二象性

Light exhibits both wave-like and particle-like behaviour, known as wave-particle duality. In IB Physics, we primarily explore its wave properties—reflection, refraction, interference, diffraction, and polarization. Visible light is electromagnetic radiation with wavelengths ranging from approximately 400 nm (violet) to 700 nm (red). The speed of light in a vacuum, c = 3.00 × 10⁸ m s⁻¹, is a fundamental constant that relates frequency f and wavelength λ via c = fλ.

光表现出波动性和粒子性，即波粒二象性。在 IB 物理中，我们主要研究其波动性质——反射、折射、干涉、衍射和偏振。可见光是波长约在 400 nm（紫光）到 700 nm（红光）之间的电磁辐射。真空中的光速 c = 3.00 × 10⁸ m s⁻¹ 是一个基本常数，它将频率 f 和波长 λ 通过 c = fλ 联系起来。

2. Reflection and the Law of Reflection | 反射与反射定律

When light strikes a smooth surface, it bounces back according to the law of reflection: the angle of incidence (θᵢ) equals the angle of reflection (θᵣ), both measured from the normal to the surface. This principle forms the basis for image formation in plane mirrors, where the image is virtual, upright, and laterally inverted, located the same distance behind the mirror as the object is in front.

当光照射到光滑表面时，会按照反射定律反弹：入射角（θᵢ）等于反射角（θᵣ），两者都从法线量起。这一原理是平面镜成像的基础，平面镜所成的像是虚像、正立、左右颠倒，且位于镜后与物到镜面等距的位置。

3. Refraction and Snell’s Law | 折射与斯涅尔定律

Refraction occurs when light passes from one medium to another, changing speed and direction. Snell’s law relates the incident and refracted angles: n₁ sin θ₁ = n₂ sin θ₂, where n is the refractive index. The absolute refractive index of a medium is n = c / v, always ≥ 1. When light enters an optically denser medium, it bends toward the normal. A typical exam problem asks you to calculate the angle of refraction as light travels from air into glass.

折射发生在光从一种介质进入另一种介质、速度与方向发生改变时。斯涅尔定律将入射角和折射角联系起来：n₁ sin θ₁ = n₂ sin θ₂，其中 n 为折射率。介质的绝对折射率为 n = c / v，总是 ≥ 1。当光进入光密介质时，光线向法线偏折。典型的考题会要求计算光从空气进入玻璃时的折射角。

4. Total Internal Reflection & Critical Angle | 全内反射与临界角

When light travels from a denser medium to a less dense one, total internal reflection (TIR) occurs if the angle of incidence exceeds the critical angle θ_c. The critical angle is given by sin θ_c = n₂ / n₁, where n₁ > n₂. TIR is the principle behind optical fibres, which transmit light pulses over long distances with minimal loss. In data communications and endoscopy, this phenomenon is essential.

当光从光密介质射向光疏介质且入射角大于临界角 θ_c 时，会发生全内反射（TIR）。临界角由 sin θ_c = n₂ / n₁ 给出，其中 n₁ > n₂。TIR 是光纤的工作原理，光纤可将光脉冲以极低损耗长距离传输。在数据通信和内窥镜检查中，这一现象至关重要。

5. Lenses and the Thin Lens Equation | 透镜与薄透镜公式

Converging (convex) lenses bring parallel rays to a focus, while diverging (concave) lenses spread them out. Ray diagrams use three principal rays to locate the image. The thin lens equation is 1/f = 1/u + 1/v, where f is focal length, u is object distance, and v is image distance. The sign convention: for convex lenses f > 0; for concave lenses f < 0. Magnification m = v/u gives both size and orientation – a negative m indicates an inverted image. Always remember that a virtual image has a negative v.

会聚透镜（凸透镜）将平行光线

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