Question

A astronomical telescope has objective and eyepiece of focal length 40 cm and 4 cm resp. To view an object 200cm away from the objevtive , the lenses must be separated by a distance.

Ans) 54.0 cm
plzz tell me the mechanism to solve this question.

Answer 1

Focal length of the objective lens, Fo = +40 cm 
Focal length of eyepiece, Fe = 4 cm 
Object distance for objective lens (uo) = -200 cm 
,Applying lens formula for objective lens,


 
 

Image will be formed at the focus of a eyepiece lens. 

So, for normal adjustment distance between objectives and eyepiece (length of tube) will be,



Answer 2

this may help u........