Question

A astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance:(a) 37.3 cm(b) 46.0 cm(c) 50.0 cm(d) 54.0 cm

Answer 1

(c) 50.0 CM is the answer

Answer 2

Answer:

D) 54cm

Explanation:

The focal length of the objective lens, Fo = +40 cm  

The focal length of eyepiece, Fe = 4 cm  

Object distance for objective lens (uo) = -200 cm  

Applying lens formula for objective lens -

1/v-1/u = 1/f

1/v- 1/-200 = 1/40

1/v = 1/40-1/200

= 5-1/200

= 4/200

= 1/50

Thus v = 50cm

Therefore, the image will be formed at the focus of eyepiece lens

So, for normal adjustment the distance between objectives and length of tube ( eyepiece) is -

v+Fe = 50+4 = 54cm

Thus, the lenses must be separated by a distance of 54cm