光為甚麼會反射,折射,散射?

折射其實可以諗成一個物體從空氣入到水入面，因為密度唔同…物體既速度同方向會有所影響????

折射是一個光學名詞，指光從一種介質進入另一種具有不同折射率之介質，或者在同一種介質中折射率不同的部分運行時，由於波速的差異，使光的運行方向改變的現象。例如當一條木棒插在水裡面時，單用肉眼看會以為木棒進入水中時折曲了，這是光進入水裡面時，產生折射，才帶來這種效果。

Reflection, refraction, diffraction and scattering are all properties of waves. The particle nature of light in terms of photons is NOT a suitable physical concept in explaining wave properties. The theory of light photons is more applicable in qunatum mechanical situations.
Simply speaking, light is, in fact, electromagentic waves in nature. The travelling of light in a medium (including free space) is due to mutual interaction of electric and magnetic fields. The speed of light, and lots of its properties, are therefore depend very much on the electric and magnetic properties of the medium in which light travels. These electric and magentic properties determine the various wave properties of light.
仲有,天空為甚麼是藍色
This is due to scattering of sun light by fine dust particles (which is called aerosoles) in the air. When light rays incident onto a fine particle, the light ray will be "diverted" to all direction, this process is called scattering. Rayleight discovered that such scattering depends inversely as the 4th power of wavelength.
Blue light, having wavelength shorter than other colour lights, undergoes more scattering than other colour lights. Thus the sky looks blue because of the scattered blue light.
You may refer to the following web-page for more information:
http://hyperphysics.phy-astr.gsu.edu/Hbase/atmos/blusky.html

其實物理上既定理有好多野都唔可以解釋到。
不過折射其實可以諗成一個物體從空氣入到水入面，因為密度唔同…物體既速度同方向會有所影響。