PURPOSE: To determine the location of a real image in a complex lens-mirror system.

DESCRIPTION: A lens has a focal length twice that of a convex mirror. The lens is positioned at a distance of twice the focal length of the mirror (the focal length of the lens) in front of the mirror. An object is placed a distance of twice the focal length of the lens in front of the lens. The image position, at the same point as the object position, can be determined by calculation and verified by this demonstration. The photograph below shows the real, inverted image on the baffle.

SUGGESTIONS: This was a question on an examination for engineering physics, after which the students viewed the image using this setup to see that the system actually works! See Question of the Week #304 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA unknown.) See Demonstration Reference File for further information, including the exam question and the complete solution.

EQUIPMENT: Light source with small arrow/circle object baffle, 60cm focal length convex lens, and 26.3cm focal length convex mirror, on two meter optical rail.

SETUP TIME: 5 min.