# 光

(已重新導向自 光線)

## 研究歷史

### 電磁理論

1845年，麥可·法拉第發現當偏振光穿過施加了磁場的透明介質時，會發生偏振旋轉。這後來被稱為法拉第效應，它首次發現了光和電磁的關係。在1846年，他推測光可能是沿磁場線衍生的某種形式的擾動。次年，法拉第提出光是一種高頻電磁振動，不需要介質也能衍生。

## 特性

### 反射

1. 反射線、入射線與法線在同一平面上。
2. 反射線與入射線在法線的兩側。
3. 反射角等於入射角：
$\angle \theta_i = \angle \theta_r$

### 折射

$n_1 \sin \angle \theta_1 = n_2 \sin \angle \theta_2$

$v_2 = v_1 \tfrac {\sin \angle \theta_2}{\sin \angle \theta_1}$

$\angle \theta_2 = 90^\circ$ 時，折射光沿著介面運行，這時 $\angle \theta_1$ 稱為臨界角 $(\angle \theta_c)$；當 $\angle \theta_1 > \angle \theta_c$ 時，入射光則完全反射回原介質，稱為全內反射。

## 參考文獻

1. ^ International Commission on Illumination (1987). International Lighting Vocabulary. Number 17.4. CIE, 4th edition. ISBN 978-3-900734-07-7.
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."
4. ^ Laufer, Gabriel. Introduction to Optics and Lasers in Engineering. Cambridge University Press. 13 July 1996: 11 [20 October 2013]. ISBN 978-0-521-45233-5.
5. ^ Bradt, Hale. Astronomy Methods: A Physical Approach to Astronomical Observations. Cambridge University Press. 2004: 26 [20 October 2013]. ISBN 978-0-521-53551-9.
6. ^ Ohannesian, Lena; Streeter, Anthony. Handbook of Pharmaceutical Analysis. CRC Press. 9 November 2001: 187 [20 October 2013]. ISBN 978-0-8247-4194-5.
7. ^ Ahluwalia, V. K.; Goyal, Madhuri. A Textbook of Organic Chemistry. Narosa. 1 January 2000: 110 [20 October 2013]. ISBN 978-81-7319-159-6.
8. ^ Hecht, Eugene, Optics 4th, United States of America: Addison Wesley, pp. 106–111, 141, 2002, ISBN 0-8053-8566-5 （English）