Question

A telescope is formed from an objective lens of focal length 60 cm and an eyepiece of focal length 5 cm. It is focused on a distant object in such away that parallel rays emerge out of the eyepiece.If the object subtends an angle of 2${}^{\circ }$ at the objective then the angular width of image will be

• A. 50${}^{\circ }$
• B. 10${}^{\circ }$
• C. 24${}^{\circ }$
• D. 20${}^{\circ }$

Answer 1

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

$f_o=60cm$

$u_e=f_e$

$f_e=5cm$

$m_{\infty }=\frac{f_o}{f_e}=\frac{|\beta |}{|\alpha |}$

$L_{\infty }=f_o+f_e$

$\frac{60}{5}=\frac{|\beta |}{|2|}$

$\beta ={24}^0$