Question

An astronomical telescope of tenfold angular magnification has a length of 4.4 cm. The focal Iength of the objective is

(a) 44 cm

(b) 440 cm

(c) 4 cm

(d) 40 cm

Answer 1

Correct option  (d) 40 cm

Explanation:

Length of astronomical telescope (f₀ + f_e) = 44 cm and ratio of focal length of the objective lens to that of the eye piece f₀/f_e =10

From the given ratio, we find that f₀ = 10 f_e.

Therefore 10f_e + .f_e = 44 or f_e = 4 cm and focal length of the objective (f₀)

= 44 - f_e = 44 - 4 = 40