In an astronomical telescope in normal adjustment a straight black line of length `L` is drawn on inside part of objective lens. The eye piece forms a real image of this line. The length of this image is `I`. The magnification of the telescope is

Options

A. `(L)/(I)`
B. `(L)/(I) + 1`
C. `(L)/(I) - 1`
D. `(L + I)/(L - I)`

Answer

A

Explanation

Magnification by eye piece, `m = (f)/(f + u)`
As, `m = (h_(2))/(h_(1)) = (-I)/(L) = (f_(e))/(f_(e) + (-(f_(0) + f_(e))))`
`-(I)/(L) = -(f_(e))/(f_(0))`
Magnifying power of telescope `= (f_(0))/(f_(e)) = (L)/(I)`