The system contains a box of length L = 20cm. On the left end of the box, a plane mirror is placed and on the right hand a convex lens of focal length f is placed. An object is placed at a distance 'x' from the plane mirror. Two images are formed for the system. One is direct refraction through the lens and other is after reflection from plane mirror and then refraction through the lens. The size of final images formed is same. Find the focal length of the lens.
