Question

A simple telescope consisting of an objective lens of focal length $60 \, cm$ and an eye lens of focal length $5 \, cm$ , is focused on a distant object. If the object subtends an angle of $2^\circ $ at the objective lens, the angular width of the image is

• A. $50^\circ $
• B. $\left(\frac{1}{6}\right)^\circ $
• C. $10^\circ $
• D. $24^\circ $

Answer 1

Answer: (D)

Magnifying power for normal adjustment (distant object) is given by,
$M.P.=\frac{\beta }{\alpha }=\frac{f_{o}}{f_{e}}$
$\Rightarrow \frac{\beta }{2}=\frac{60}{5}$
$\Rightarrow \beta =24^\circ $