Question

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

• A. 10${}^o$
• B. 24${}^o$
• C. 50${}^o$
• D. (1/6)${}^o$

Answer 1

The correct option is B 24${}^o$

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

$\therefore \beta =\frac{f_0}{f_e}\alpha =\frac{60}{5}\times 2^o={24}^o$