Question

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

• A. ${10}^o$
• B. ${24}^o$
• C. ${50}^o$
• D. ${60}^o$

Answer 1

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

Given, the Focal length of the objective lens is $f_0=60cm$

The focal length of the eye lens is $f_e=5cm,Angle=2^0$

Therefore,

$M=\beta =\frac{f_0}{f_e}\Rightarrow \frac{60}{5}\times 2={24}^0$