物理一問 折射定律

ng = sin i / sin r
假設是有光線由空氣進入玻璃glass 或 水
空氣果個角放sin i位

下例以
θ1 為 i , θ2 為 r
光線 由介面1 進入 介面2

折射定律 - 斯涅爾定律 Snell's Law
n1sinθ1 = n2sinθ2

圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/3/3f/Snells_law2.svg/180px-Snells_law2.svg.png

簡化的寫法
1n2 = sinθ1 / sinθ2
會是 ng = sin i / sin r
介面1 是空氣/真空, 介面2 glass 玻璃,


**注意
一般的折射是有 "可逆性", 即光線路線不變, 但反向
即 2n1 = sinθ2 / sinθ1

http://zh.wikipedia.org/w/index.php?title=%E6%8A%98%E5%B0%84%E5%AE%9A%E5%BE%8B&variant=zh-hk


2009-05-31 14:32:04 補充：
中學的課本為了簡化公式會寫

玻璃的折射率為 (eta g) ng = sin i / sin r

[空氣果個角放sin i位]

e.g.
ng = sin i / sin r
玻璃折射率~=1.5
當i=50度時,
1.5 = sin 50 / sin r
sin r = 0.51
r= 30.7度

the symbol "i" denotes the incident angle disregard the medium is air or other materials.
For example, if light ray travels from air to water, then the incident angle i is the angle in the air medium.
Likewise, if the light ray travels from water to air, then the incident angle i is the angle in the water medium.
It is because of theis reason that
refractive index(air --> water) = 1/refractive index(water --> air)