Question

Two thin plano-convex lenses each of focal length $f$ are placed as shown in the figure. The ratio of their effective focal lengths in the three cases is

• A. 3:02:01
• B. 1:02:03
• C. 1:02:01
• D. 1:01:01

Answer 1

Answer: (D)

1:01:01

Answer 2

Effective focal length in each case is given by
$\frac{1}{F} = \frac{1}{f}+\frac{1}{f}$ or $F = \frac{f}{2}$