Question

An astronomical telescope has objective and eye-piece lenses of powers 0.5 D and 20 D respectively. What will be its magnifying power ?

• A. 30
• B. 10
• C. 40
• D. 20

Answer 1

The correct option is C 40

Given, the power of objective lens,
$P_o=0.5D$
The power of eye-piece lens,
$P_e=20D$
The magnifying power of an astronomical telescope
$M=\frac{f_o}{f_e}$
or $=\frac{P_e}{P_o}$ $[\therefore P=\frac{1}{f}]$
$=\frac{20}{0.5}=40$