Two thin lenses are of same focal lengths (f), but one is convex and the other one is concave. When they are placed in contact with each other, the equivalent focal length of the combination will be:

Option 1 -

Infinite

Option 2 -

Zero

Option 3 -

$\frac{f}{4}$

Option 4 -

$\frac{f}{2}$

2 Views | Posted a month ago

Asked by Shiksha User

1 Answer

Answered by

Raj Pandey | Contributor-Level 9

a month ago

Correct Option - 1

Detailed Solution:

$F_{convex} = f$

$F_{concave} = - f$

$\begin{array}{r} \frac{1}{f_{comb}} = \frac{1}{F_{convex}} + \frac{1}{F_{concave}} \\ = \frac{1}{f} - \frac{1}{f} \end{array}$

$\Rightarrow f_{comb} = \infty$

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Two thin lenses are of same focal lengths (f), but one is convex and the other one is concave. When they are placed in contact with each other, the equivalent focal length of the combination will be:

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