Question

(i) Define magnifying power of a telescope. 

(ii) Write its expression. A small telescope has an objective lens of focal length 150 cm and an eyepiece of focal length 5 cm. If this telescope is used to view a 100 m high tower 3 x 10⁵ cm away, find the height of the final image when it is formed 25 cm away from the eye piece.

Answer 1

(i) Magnifying power is the ratio of the angle subtended at the eye by the image to the angle subtended at the unaided eye by the object.

Using lens formula for eyepiece,

= 30 x 10^-4 x 100 m

= 30 cm