Task id16296

A converging lens is inserted into a round hole in an opaque screen. A point light source is located on the main optical axis of the lens at a distance d = 10 cm from it. On the other side of the lens, at the same distance d from it, a screen is placed perpendicular to this axis. A light circle is visible on the screen, the diameter of which is n = 2 times less than the diameter of the lens. Determine the focal length of the lens F.