# A convex lens, of focal length 30 cm, a concave lens of focal length 120 cm, and a plane mirror are arranged as shown. For an object kept a distance of 60 cm from the convex lens, the final image, formed by the combination, is a real image, at a distance of :

Thin lens formula -

$\frac{1}{v}-\frac{1}{u}= \frac{1}{f}$

$u \, and \, v$ are object and image distance from lens.

Len's formula is given by

$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

For convex lens = $\frac{1}{30}=\frac{1}{v}+\frac{1}{60}=\frac{1}{60}=\frac{1}{v}$

For concanve lens = $\frac{1}{-120}=\frac{1}{v}-\frac{1}{40}=\frac{1}{v}=\frac{1}{60}$

Virtual object 10 cm behind plane mirror.

Hence real image 10 cm infront of mirror or 60 cm from convex lens.

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