Q. A simple microscope consists of a concave lens of power $- 10$D and a convex lens of power +20D in contact. If the image is formed at infinity, then the magnifying power $CD = 25\ $cm is
A) 2.5
B) 3.5
C) 2.0
D) 3.0
Explanation
(a) Power of combination $P = P_{1} + P_{2}$
$= + 20 - 10 = + 10D$
$F = \frac{1}{P} = \frac{1}{10}$m =10 cm
For image at infinity
$M = \frac{D}{F} = \frac{25}{10} = 2.5$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.