Q. The power of the combination of a convex lens of focal length 50 cm and concave lens of focal length 40 cm is
A) +1 D
B) -1 D
C) Zero
D) -0.5 D
Explanation
(d) $P = P_{1} + P_{2}$
=$\frac{100}{f_{1}} + \frac{100}{f_{2}}$, both $f_{1}$ and $f_{2}$ are in cm.
$= \frac{100}{50} - \frac{100}{40}$
=2-2.5=-0.5 D
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.