27 Jun, 2013
PRESENTACIÓN: Two concave mirrors are placed so that their poles are separated by half (or three halves) of their radius of curvature. A hole is made in the pole of the top mirror in which the real direct image and the inverted virtual image of a small object located at the pole of the bottom mirror are seen.
- Real image produced by a concave mirror, Robert M. Graham, Phys. Teach. 44, 186 (2006)
- Concave liquid-mirror experiments, Hugo Graumann and Hans Laue, Phys. Teach. 36, 28 (1998)
- Teaching geometrical optics with the ‘‘optic mirage’’, Andrzej Sieradzan, Phys. Teach. 28, 534 (1990)
INTRODUCTION: the mirage has an interesting history: it begins with an accidental observation by a cleaner at the Department of Physics of the University of California four decades ago. He was cleaning a pile of big reflecting mirrors from the Second World War. These mirrors have a central opening for the lamp base. He was surprised at seeing a realistic illusion of “dust which could not be cleaned.” He informed a member of the department who quickly recognized the optical principles. This meant a novelty and the potential utility of this kind of devices for the analysis of jewelry, among other applications.
OBJECTIVE: to test that an optical illusion is created with two concave mirrors facing each other.
MATERIALS: two concave mirrors, one of them with a small hole in its center, a small-size object.
SETUP: a small size object is placed on one of the concave mirrors and above this the other mirror is placed, and on this is set another mirror which presents a hole in its superior part, where the object mentioned before can be seen.
EXPLANATION: The object is placed in the center of the lower mirror, which is covered by the mirror which has the hole. The curvature of the mirrors is such that the object is in the focal point of the upper mirror. When the light falls upon the object, the upper mirror reflects its rays towards the lower mirror where they are reflected again in such a way that they give shape to an image in a point placed at the focal distance of the lower mirror. The final result is that the light of each point object is assembled into a real image in the hole.
As a curiosity: if a piece of onionskin paper is placed in the location of a real image, that image will not appear. The external regions of the mirrors reflect the light on the paper. The borders of the mirrors have big aberrations and create such a blurred image that cannot be seen.
CONCEPTS: Concave mirror, focal object and image, real and virtual image.
- YOUTUBE 1
- YOUTUBE 2
- TEXAS UNIVERSITY
- UNIVERSITY OF NORTH TEXAS
- BERKELEY UNIVERSITY
- Tipler P.A. Física, Reverté, 2010.
- De Juana J.M., Física General, Pearson, 2009.
- Serway R.A, Jewett J.W., Física, Thomson-Paraninfo, 2010.
STUDENTS 2012-2013: Nuria Mouronte, Carlos Macho.
LINK pdf STUDENTS (in Spanish):