為甚麼CD表面會有彩虹7色?

CD為什麼反射出彩虹的顏色？
當觀察CD表面或者肥皂泡，或者觀察靜止的水面上漂浮的一薄層油時，您通常會看到彩虹圖案。 這三種效應都是由光照到薄膜上的相長干涉和相消干涉現象造成的。
由於CD的表面如同鏡面，所以彩虹色就會強烈得多。 對CD而言， CD被放置的角度決定了您所看到的顏色——因為角度會控製程差。
以水面上漂浮的一薄層油為例。當白光照到薄膜，大部分白光會穿過它，但也有一部分在薄膜的頂層和底層被反射掉。


圖片參考：http://static.bowenwang.com.cn/gif/oil-film.gif



2009-05-10 16:10:09 補充：
It is very common to see rainbow patterns when you look at the surface of a CD, and also when you look at soap bubbles or a thin film of oil floating on still water.



http://electronics.howstuffworks.com/question52.htm

You may refer to the following website:
http://hk.knowledge.yahoo.com/question/question?qid=7009010100574

It is not refraction effect. It is because of "thin film interference".
There is a very thin (almost transparent) plastic layer on top of an aluminium base on each CD. Light incident on the top and bottom of the plastic layer is reflected and interfere with each other.
If the extra distance travelled by the light reflected at the bottom of the plastic layer is a whole number of wavelengths, then constructive interference will occur.
Since white light consists of a range of wavelengths, each colour has a different wavelength. Depending on the thickness of the layer and the angle of view, there will be some places where the extra distances travelled is an exact number of, say, green wavlength and some where it is an exact number of red wavelength. This resulted in seeing a coloured light band on a CD.