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Power and Thin Lenses in Contact

If two thin l...

Question

If two thin lenses of focal length $f_{1}$ and $f_{2}$ are kept in contact to each other, then the equivalent focal length of the combination

\frac{f_{1} f_{2}}{f_{1} + f_{2}}

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\frac{f_{1} f_{2}}{f_{1} - f_{2}}

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\frac{f_{1} + f_{2}}{f_{1} f_{2}}

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\frac{f_{1} - f_{2}}{f_{1} f_{2}}

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Solution

The correct option is A $\frac{f_{1} f_{2}}{f_{1} + f_{2}}$
Net Power of a combination of lens is sum of their individual power i.e.
$P_{n e t} = P_{1} + P_{2}$
$\frac{1}{f_{n e t}} = \frac{1}{f_{1}} + \frac{1}{f_{2}}$
$f_{n e t} = \frac{f_{1} + f_{2}}{f_{1} f_{2}}$
$f_{n e t} = \frac{f_{1} f_{2}}{f_{1} + f_{2}}$

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Similar questions

Two thin lenses of focal lengths $f_{1}$ and $f_{2}$ are placed in contact with each other. The focal length of the combination will be given by:

If two thin lenses of focal length f₁ and f₂ are held in contact then the focal length of the combination will be

f_{1}

f_{2}

f_{1} a n d f_{2}

d < f_{1}, d < f_{2}

Δ

^{'} f^{'}

^{'} f^{'}

\frac{1}{F} = \frac{1}{f_{1}} + \frac{1}{f_{2}} - \frac{d}{f_{1} f_{2}}

F =

f_{1}

f_{2}

^{'} d^{'}

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