An astronomical telescope has an angular magnification of magnitude 5 for distant objects. The separation between the objective and the eye piece is 36 cm and the final image is formed at infinity. The focal length $f_0$ of the objective and the length $f_e$ of the eye piece are
Answer & explanation
Correct answer: option 4
We know that, $f_0 + f_e = 36$ …(1)
Where $l$ = length of the tube = 36 cm
$\frac{f_0}{f_e}=m=5$ …(2)
Where m = magnification = 5
Solving (1) and (2) we obtain,
$5\, f_e + f_e = 36$
$⇒ f_e = 6 cm\, and\, f_0 = 5\, f_e = 30 cm$
∴ (D)