Question

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

• A. ${10}^{\circ }$
• B. ${24}^{\circ }$
• C. ${50}^{\circ }$
• D. None of the above

Answer 1

The correct option is B ${24}^{\circ }$

Magnification, $m=\frac{-f_o}{f_e}=\frac{-60}{5}=-12$
Angular magnification, $m=\frac{\theta }{{\theta }_0}\Rightarrow 12=\frac{\theta }{2^{\circ }}\Rightarrow \theta ={24}^{\circ }$