Question: A plano-convex lens of refractive index 1.5 and radius of curvature 30 cm is silvered at the curved ...

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 the size of the object ?

Answer 1

Solution

Focal length of system (concave mirror)

F = = $\frac { 30 } { 2 \times 1.5 }$ = 10 cm

In order to have a real image of the same size of the object, object must be placed at 2f.

u = 2f = 2 × 10 = 20 cm

u = 20 cm