Single Choice

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 at a distance of $$60 cm$$ from the convex lens, the final image, formed by the combination, is a real image, at a distance of :

A$$60 cm$$ from the concave lens
Correct Answer
B$$70 cm$$ from the convex lens
C$$60 cm$$ from the convex lens
D$$70 cm$$ from the concave lens

Solution

Location of image formation after first refraction from the lens,

$$\dfrac { 1 }{ v } +\dfrac { 1 }{ 60 } =\dfrac { 1 }{ 30 } $$.

This gives $$v=60cm$$

Next refraction from concave lens,

$$\dfrac { 1 }{ v_{2} } -\dfrac { 1 }{ 40 } =-\dfrac { 1 }{ 120 } $$

Hence $${ v }_{ 2 }=60cm$$

Since this will be formed behind the mirror, this will be final image.

It is at a distance of $$60cm$$ from the concave lens.

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