Question

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

Answer 1

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

(b) Using, the lens equation for objective lens.

Hence, magnification due to the objective lens

Hence, size of final image = 30 × 10^–4 × 100m = 30cm