PURPOSE: To calculate the position of a virtual image and the verify this by using parallax.

DESCRIPTION: A concave mirror and a concave lens with the same focal length are positioned one focal length apart and the object post is positioned one focal length in front of the lens. The location of the image, behind the mirror, can be calculated and then verified experimentally using this demonstration. The image is located at the position of the rod at the left of the optical rail above (behind the mirror), which can be verified by parallax viewing between the image and the rod at that position.

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!

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

EQUIPMENT: Mounting pin parallax image, 30 cm focal length concave mirror, 30 cm focal length concave lens, and rod for object.

SETUP TIME: 5 min.

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