In a reflecting telescope, the focal length of the eyepiece is 5 cm. What should be the radius of curvature of the objective mirror to have magnifying power of 40?
Answer & explanation
Correct answer: option 3
Magnification of reflecting telescope is
$M = \frac{f_0}{f_e}$ = $\frac{f_0}{5 cm}$
$⇒ f_0 = 200 cm $
$⇒ R = 2 f_0 = 400 cm = 4m$