Question

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

• A. $60cm$ from the concave lens
• B. $70cm$ from the convex lens
• C. $60cm$ from the convex lens
• D. $70cm$ from the concave lens

Answer 1

Answer: (A)

$60cm$ from the concave lens

Location of image formation after first refraction from the lens,

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

This gives $v=60cm$

Next refraction from concave lens,

$\frac{1}{v_2}-\frac{1}{40}=-\frac{1}{120}$

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.