Question

An astronomical telescope uses two lenses of powers 10 dioptre and 1 dioptre. If the final image of a distant is formed at infinity, calculate the length of the telescope.

Answer 1

We know $m=\frac{f_o}{f_e}$
We know $P=\frac{1}{f}$
$10=\frac{1}{f_e}$
$f_e=0.1m=10cm$
for objective lens $P=\frac{1}{f}$
$f=\frac{1}{1}1m=100cm.$
So, $L=f_o+f_e$
$=100+10=110cm$