Question

An astronomical telescope has an angular magnification of magnitude 5 for distant object. The separation between the objective and the eyepiece is 36 cm and the final image is formed at infinity. The focal length `f_(0)` of the objective and the focal length `f_(0)` of the eyepiece are
A. `f_(o)=45cm` and `f_(e)=-9cm`
B. `f_(o)=7.2cm` and `f_(e)=5cm`
C. `f_(o)=50cm` and `f_(e)=10cm`
D. `f_(o)=30cm` and `f_(e)=6cm`

Answer 1

Correct Answer - D
In this case `|m|=(f_(o))/(f_(e))=5` …(i)
and length of telescope `=f_(o)+f_(e)=36` …(ii)
Solving `(i)` and `(ii)` , we get `f_(e)=6cm, f_(o)=60cm`