An astronomical telescope has an angular magnification of magnitude 5 for far objects…

Q: An astronomical telescope has an angular magnification of magnitude 5 for far objects. The separation between the objective and the eyepiece is 36 cm and the final image is formed at infinity. The focal length fo of the objective and the focal length fe of the eyepiece are

(A) fo = 45 cm and fe = – 9 cm

(B) fo = 50 cm and fe = 10 cm

(C) fo = 7.2 cm and fe = 5 cm

(D) fo = 30 cm and fe = 6 cm

Ans: (D)

Sol: $\large \frac{f_o}{f_e} = 5$ …(i)

$\large f_o + f_e = 36 $ …(ii)

On solving , we get

fo = 30 cm and fe = 6 cm