Question

A system consists of a thin symmetrical converging glass lens with the curvature radius of its surfaces R = 38 cm and a plane mirror oriented at right angles to the optical axis of the lens. The distance between the lens and the mirror is l = 12 cm. What is the optical power of this system when the space between the lens and the mirror is filled up with water?

Answer 1

The plane mirror forms the image of the lens, and water, filled in the space between the two, behind the mirror, as shown in the figure.

So, the whole optical system is equivalent to two similar lenses, separated by a distance 2l and thus, the power of this system,

= optical power of individual lens and n = R.I. of water. 

Now, Φ' = optical power of first convex surface + optical power of second concave surface.