Question

An object is placed 15 cm in front of a convex lens of focal length 10 cm. Find the nature and position of the image formed. Where should a concave mirror of radius of curvature 20 cm be placed so that the final image is formed at the position of the object itself?

Answer 1

For a convex lens, we have u = −15 cm and f = 10 cm

The mirror formula is

$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\frac{1}{v}=\frac{1}{f}-\frac{1}{u}\frac{1}{v}-\frac{1}{10}+\frac{1}{15}v=6cm$

The image is smaller in size, virtual and erect. The position of the image is at 6 cm to the right of the mirror

The final image is formed at the position of the object itself when an object lies at the centre of curvature, but the image will be real and inverted in nature. So, the concave mirror should be placed at 20 cm from the pole.