Question

In a compound microscope the objective and eye-piece have focal lengths of $0.95 cm$ and $5 cm$ respectively and are kept at distance of $20 cm .$ The last image is at $\infty$. Calculate magnifying power.

• A. 95
• B. 94
• C. $94 / 6$
• D. None of these

Answer 1

Answer: (D)

If final image is at $\infty$
then $u _{ e }=5 cm , v _{0}=20-5=15 cm$
$MP = m _{0} \times m _{e}=\left(\frac{ f _{0}- v _{0}}{ f _{0}}\right)\left(\frac{ D }{ f _{ e }}\right)$
$=\left(\frac{0.95-15}{0.95}\right)\left(\frac{25}{5}\right) \approx-74$