Question

A plano convex lens of refractive index 1.5 and radius of curvature 30 cm. Is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of size of the object
(a) 60 cm (b) 30 cm (c) 20 cm (d) 80 cm

Answer 1

For the image to be real and of same size as object, final image should be formed at the position of object itself. Let x be the distance of object from plane surface. Apparent distance from surface = μx 

This should be centre of curve μx = 30 ⇒ 1.5x = 30 ⇒x = 20