> Q. A convex and a concave lens seperated by distance $d$ are then put in contact. The focal length of the combination – LIVE ANSWER TODAY

Q. A convex and a concave lens seperated by distance $d$ are then put in contact. The focal length of the combination

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A convex and a concave lens seperated by distance $d$ are then put in contact. The focal length of the combination

Solution:

When two lenses are placed coaxially at a distance $d$ from each other, then equivalent focal length $(F)$ is given by

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

When the lenses are put together.

$d=0$

Hence, the focal length of the combination will decrease.

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