Question

an astronomical telescope consists of two thin convex lens A and B placed 36 cm apart and has a magnifying power 8 in normal adjustments. what will be the focal lengths of two lenses?

Answer 1

In normal adjustment the image forms at infinity

So f o +f e

=36 , o is for objective and and e for eye piece

Also magnification is 8

8= fe/f o

f o =8f e

on solving we get fo

=32cmf e

=4cm