Physics: real image & virtual image

在convex lens的情況下，除了個object放在within focal length (F') 下，都會出real image

剩下的都出virtual image。



在concave lens的情況下，所以image都是virtual的。



Real image 的特點
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當rays 與經過lens後focus在一點後, real image便會產生。

注意，real image是能用screen來擋著, 並在screen上看見那個image。


(That means the rays actually meet at the image and a real image can be captured on a screen)



Virtual image 的特點
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Rays 並沒有focus再任何一點，只是rays經過lens後你會看到image的原因是因為我們

眼睛看到那些rays好像從virtual image射出，但其實這個image並不實在。那就是說那個

image不能用screen來擋著來看到，因為那image根本不存在。


(That means a virtual image cannot be captured on a screen and the rays appear to come from the image.)



主要的分別就是一個能capture on a screen, 一個不能了。

能Capture on a screen能表示那image的確存在，但virtual image則只是一種視覺上的誤差了。

real image : inverted,diminished
only formed by convex lens
However, when the object between the 2F and F, the image formed is real, inverted and magnified.
When it's at the focal length less than F, it's virtual, erect and magnified.


virtual image : erect
Formed by concave lens: diminished
Formed by convex lens : magnified

To distinguish between real and virtual is very easy,
**A real image can be caught by screen while virtual cannot.
**A real image is inverted while a virtual image is erect.


The image formed by mirror is virtual.

At TV, I think it's nothing concern with the kind of image formed but electrical signls.

real image 可以在一張紙上成像[can form image on screen/paper].但virtual image則不可以
咁在鏡子入面的影像是real or virtual? Virtual, due to unable to form image on a screen or paper.

電視入面又係咩? the image is formed by screening of electron bean controlled by a vertical circuit and horizontal circuit. It is just an electric signal coming from the TV station which can't be compared with the 鏡子入面的影像是real or virtual

2007-01-22 18:56:30 補充：
Any image that is formed form the converging of light line聚合的光線(不用虛線去聚焦成一點,然後去畫像),就是真像,real such as convex lens and concave mirror.Any image that is formed form the diverging of light line發散的光線(用虛線去繪聚焦成一點,然後去畫像),就是假像,virtual such as cocave lens and convex mirror.你自己繪一繪出來即可明白在下說些什麼