Question

The focal lengths of objective and eye lens of anastronomical telescope are respectively $2m$ and $5cm$. Final image is formed at (i) least distance of distinct vision, (ii) Infinity. Magnifying power in two cases will be:

• A. $-48,-40$
• B. $-40,-48$
• C. $-40,+48$
• D. $-48,+40$

Answer 1

The correct option is A $-48,-40$

$\left(i\right)M=\frac{f_o}{f_e}=\frac{5}{2m}\frac{200}{5}=-40$

$\left(ii\right)M=\frac{-f_o}{f_e}(1+\frac{5}{25})=-40\left[\frac{30}{25}\right]=-48$