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  • (a) Draw a labelled ray diagram to obtain the real image formed by an astronomical telescope in normal adjustment position. Define its magnifying power. (b) You are given three lenses of power 0.5 D , D and 10 D to design a telescope. (i)

(a) Draw a labelled ray diagram to obtain the real image formed by an astronomical telescope in normal adjustment position. Define its magnifying power.
(b) You are given three lenses of power 0.5 D , D and 10 D to design a telescope.
(i) Which lenses should he used as objective and eyepiece? Justify your answer.
(ii) Why is the aperture of the objective prefered to be large?

 

 

 

 
 
 
 
 

Answers (1)


Magnification =  \frac{Angle\, subtended\, by\, the \, image\, at \, eye}{Angle \: subtended\, by\, object\, at\, unabded\, eye}
    M= \frac{\beta }{\alpha }= \frac{f_{0}}{f_{e}}
b) (i) objective = 5D
eye piece = 10 D
The choice gives high magnification
m= \frac{f_{0}}{f_{e }}= \frac{p_{e}}{p_{0 }}= \frac{10}{5}= 2
ii) The aperture of the objective is made larger to collect sufficient light to form a bright image of the distance object
 

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