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)))`
`[because u = -(f_0 + f_e)]`
`-(L)/(L) = -(f_e)/(f_0)`
Magnifying power of telescope `=(f_0)/(f_e) = (L)/(I)`.
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