Answer to Question #92249 in Optics for Sridhar

Question

The focal lengths of objective lens and eye lens of a Gallelian Telescope are respectively 30 cm and 3.0 cm. Telescope produces virtual, erect image of an object situated far away from it at least distance of distinct vision from the eye lens. In this condition, the Magnifying Power of the Gallelian Telescope should be
1) +11.2
2) -11.2
3) - 8.8
4) + 8.8

Answer 1

The magnifying power of astronomical telescope M is given by formula

$$M= \frac{-f}{F} × (1+\frac{F}{d_{0}}) (1)$$

where f is the focal length of objective, F is the focal length of eyepiece, d₀=0.25 m

Using (1) we get:

M=+8.8

Answer:

4) + 8.8