Confusion with angular magnification

May 2017
28
0
Sri Lanka
The angular magnification defined as,
angle subtended by image of object /angle subtended by object when 25 cm from the naked eye

Consider this.

An object is placing 50cm in front of a convex lens which has a focus length of 100cm. So the image will create 100cm in front of the lens.

If we consider the angular magnification,

angle subtended by image of object /angle subtended by object when 25 cm from the naked eye

=(h/100)/(H/25) [h=image height H=object height]

My question is this. According to the above definition this should be correct. But, according to my feelings, I feel that the meaning of the angular magnification of the lens is,

angle subtended by image of object /angle subtended by object at its own placement

That means according to above example,
=(h/100)/(H/50)

(That because according to the word 'angular magnification' I feel it is relative to its normal location angle, that is not 25cm, it is regarding to the place which is keeping the object)

What is the wrong in my thinking. Why do the definition limited the object to the least distance of eye can clearly see? Why isn't it depend on the place which the object keeps...... I am confuse with them.
 
Last edited:
Apr 2015
1,035
223
Somerset, England
Read this.

I cannot put it more clearly.

Note that 250mm is just a standard distance for comparison of the power of lenses. The magnification does indeed depend upon the object distance.

Did you note whether such an image is real or virtual?
 

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