Question

A simple telescope, consisting of an objective of focal length 60 cm and a single eye lens of focal length 5 cm is focused on a distant object in such a way that parallel rays emerge from the eye lens. If the object makes an angle of $2^o$ at the objective, then the angular width of the image is :

• A. ${10}^o$
• B. ${24}^o$
• C. ${50}^o$
• D. ${48}^o$

Answer 1

Answer: (B)

${24}^o$

Magnification by telescope, $M=\frac{f_0}{f_e}=\frac{\beta }{\alpha }$

$\beta =\frac{f_0\alpha }{f_e}$

$=\frac{60\times 2^{\circ }}{5}={24}^{\circ }$