Question

(i) Draw a ray diagram depicting the formation of the image by an astronomical telescope in normal adjustment.

(ii) You are given the following three lenses. Which two lenses will you use as an eyepiece and as an object to construct an astronomical telescope? Give reason.

Lenses	Power (D)	Aperture (cm)
L1	3	8
L2	6	1
L3	10	1

Answer 1

(i) Ray diagram of astronomical telescope

(Note: Deduce ½ mars if the ‘arrows’ are not marked)

(ii) Objective Lens: Lens L₁

Eyepiece lens: Lens L₂

Reason:

The objective should have large aperture and large focal length while the eyepiece should have small aperture and small focal length.