# 光

## 研究历史

### 电磁理论

1845年，迈克尔·法拉第发现当偏振光穿过施加了磁场的透明介质时，会发生偏振旋转。这后来被称为法拉第效应，它首次发现了光和电磁的关系。在1846年，他推测光可能是沿磁场线衍生的某种形式的扰动。次年，法拉第提出光是一种高频电磁振动，不需要介质也能衍生。

## 特性

### 反射

1. 反射线、入射线与法线在同一平面上。
2. 反射线与入射线在法线的两侧。
3. 反射角等于入射角：
${\displaystyle \angle \theta _{i}=\angle \theta _{r}}$

### 折射

${\displaystyle n_{1}\sin \angle \theta _{1}=n_{2}\sin \angle \theta _{2}}$

${\displaystyle v_{2}=v_{1}{\tfrac {\sin \angle \theta _{2}}{\sin \angle \theta _{1}}}}$

${\displaystyle \angle \theta _{2}=90^{\circ }}$ 时，折射光沿着界面运行，这时 ${\displaystyle \angle \theta _{1}}$ 称为临界角 ${\displaystyle (\angle \theta _{c})}$；当 ${\displaystyle \angle \theta _{1}>\angle \theta _{c}}$ 时，入射光则完全反射回原介质，称为全内反射。

## 参考文献

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By the International Lighting Vocabulary, the definition of light is: “Any radiation capable of causing a visual sensation directly.”
2. ^ Pal, G. K.; Pal, Pravati. chapter 52. Textbook of Practical Physiology 1st. Chennai: Orient Blackswan. 2001: 387 [11 October 2013]. ISBN 978-81-250-2021-9. The human eye has the ability to respond to all the wavelengths of light from 400-700 nm. This is called the visible part of the spectrum.
3. ^ Buser, Pierre A.; Imbert, Michel. Vision. MIT Press. 1992: 50 [11 October 2013]. ISBN 978-0-262-02336-8. Light is a special class of radiant energy embracing wavelengths between 400 and 700 nm (or mμ), or 4000 to 7000 Å.
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8. ^ 各个波段的电磁波特征与用途
9. ^ 近红外光谱仪
10. ^ X光对人体的影响
11. ^ Whittaker, E. T., A history of the theories of aether and electricity. Vol 1, Nelson, London, 1951
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13. ^