A converging lens and a diverging mirror are positioned with a separation of 15 cm . The focal length of the lens is 25 cm while that of the mirror is 40 cm . Determine where a point source must be placed between the lens and the mirror so that the light, following reflection by the mirror and subsequent transmission through the lens, emerges parallel to the principal axis.

Step-by-step solution

For the light to emerge parallel to the principal axis after passing through the converging lens, the virtual object for the lens (which is the image formed by the mirror) must lie at the focal point of the lens. Since the light travels from the mirror to the lens, the focal point of the lens for this incident light is at a distance of 25 cm from the lens, on the side of the mirror. The separation between the lens and the mirror is 15 cm . Therefore, the image formed by the mirror must be located 25 - 15 = 10 cm be