Q152 / 180 · KCET 2012 · Physics

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
$3: 2: 1$
B
$1: 2: 3$
C
$1: 2: 1$
Correct answer
D
$1: 1: 1$

Solution

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

Hence, the correct answer is option: 'D'.

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