Question

A telescope is a device that is used to magnify distant objects with a relaxed eye. One simple

telescope is made of two converging lenses where the image from the front lens, called the

objective, is the object for the back lens, called the eyepiece.

In 1655, just fifty years after Galileo

Answer 1

(a) The distance between the lenses in a simple telescope is given as the sum of the focal length of the objective lens and the focal length of the eyepiece lens.

Focal length of the objective lens, F = 340 cm = 340 cm / 100 cm/m = 3.4 m.

Focal length of the eyepiece lens, f = 80 mm = 80 mm / 1000 mm/m = 0.08 m.

The distance between the lenses, d = F + f = 3.4 + 0.08 = 3.48 m.

(b) The ray diagram for the telescope tube is given below

(c) The rays coming from the object at infinity, converge due to the objective to form a real inverted image.

The image which we receive in our eyes is a virtual image of this real image at infinity.

So the image is virtual and inverted.

The magnification of the image is given by, M = F/f = 3.4 / 0.08 = 42.5