Q. The focal length of the objective and the eye-piece of a microscope are 4 mm and 25 mm respectively. If the final image is formed at infinity and the length of the tube is 16 cm, then the magnifying power of microscope will be
A) $- 337.5$
B) $- 3.75$
C) 3.375
D) 33.75
Explanation
(a) When final image is formed at $\infty,$
$M = \frac{v_{0}}{u_{0}}\left( \frac{D}{f_{e}} \right) = \frac{v_{o}}{f_{o}}\left( \frac{D}{f_{e}} \right)$
Now,${\ v}_{o} = 16 - f_{e} = 16 - 2.5 = 13.5\ cm$
$M = \frac{13.5}{- 0.4} \times \frac{25}{2.5} = - 337.5$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.