Question

A simple telescope consisting of an objective of focal length 60 cm and single eye lens of focal length 5 cm is focused on a distant object is such a way that parallel rays come out from the eye lens. If the object subtends an angle $2^{\circ }$ at the objective, the angular width of the image :

• A. ${10}^{\circ }$
• B. ${24}^{\circ }$
• C. ${50}^{\circ }$
• D. $1/6^{\circ }$

Answer 1

Answer: (B)

${24}^{\circ }$

$m=\frac{Anglesubtendedbytheimage}{Anglesubtendedbytheobject}$
$\frac{f_0}{f}=\frac{\alpha }{\beta }$
$\Rightarrow \alpha =\frac{f_0\times \beta }{f}=\frac{60\times 2}{5}={24}^{\circ }$