A telescope has an objective of focal length `50cm` and an eyepiece of focal length `5cm.` The least distance of distinct vision is `25cm.` The telescope is focused for distinct vision on a scale `2m` away from the objective. Calculate (a) magnification produced and (b) separation between objective and eyepiece.

Options

A. `75cm`
B. `60 cm`
C. `71 cm`
D. `74 cm`

Answer

C

Explanation

`f_(o)=50cm, f_(e)=5cm, D=25cm, `and `u_(o)=200cm`.
Separation between the objective and the eye lens is
`L=(u_(o)f_(o))/((u_(o)-f_(o)))+(f_(e)D)/((f_(e)+D))`
`=(200xx50)/((200-50))+(5xx25)/((5+25))=71cm`