The focal lengths of the lenses of an astronomical telescope are `50cm` and `5cm`. The length of the telescope when the image is formed at the least distance of distinct vision is

Options

A. 45 cm
B. 55 cm
C. `275/6cm`
D. `325/6`cm

Answer

D

Explanation

(d) Length of the telescope when final image is formed at least distance of distinct vision is,
`L=f_(o)+u_(e)=f_(o)+(f_(e)D)/(f_(e)+D)=50+(5xx25)/(5+25)=325/6cm`