Summary
| Subject keyword(s) | Education, Hypothesizing, Interpreting data, Light, Mirrors, Observing, Physical science, Physics, Reflection, Science as inquiry, Science process skills |
|---|---|
| Grade level | Elementary School, Middle School, Vocational/Professional Development Education |
| Intended audience | Educator |
| Resource type | Instructional Material, Reference Material |
| Resource format | image, image/gif, text, text/html |
| Rights | The Annenberg/CPB projects http://www.learner.org/about/legal_policy.html |
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Content contained within the resource
Ever since Narcissus peered into the pond, mirrors have fascinatedus. They show us what we want to see (and what we don't), but theyalso surprise us. The main rule for mirrors is that the angle of incidence equalsthe angle of reflection. What does that mean exactly? This diagramwill help make the rule clear: To make this rule work reliably in unusual situations, you have toget this straight: the angles in question are "from the normal," thatis, they're the angle between the beam and the normal to the mirror.(What's normal? In geometry and optics, normal means"perpendicular." So the normal, or normal line, to the mirror isthe line perpendicular to it.) When the mirror is curved, the rule still holds. But how do youuse the rule to tell what the image looks like? It can be confusingto figure out just which beams of light are relevant. The key tosolving the problem is to realize that while light goes off in alldirections from every part of your body, the only beams that you seein the mirror are the ones that hit your eyes. Furthermore, the easiest beams to figure out are the ones thatcome from your eyes, bounce off the mirror, and go rightbackbecause they are normal to the mirror. The angle of incidenceis zero, so the angle of reflection is too. From this you can seethat concave mirrors make you tall (you have to look up to get aperpendicular line: your eyes appear above you) while convex make youshort (you have to look down). Curved mirrors are interesting at any age. It's good to givestudents mirrors to hold and play with. Reflective plastic sheets(e.g., Mylar) are safe and work fine. You can also get Mylar fromthose shiny party balloons. These days, you can also find highlyreflective wrapping paper. Just be sure you can see yourself well enoughbefore you buy. Even young children can experiment and figure out which kindof curve stretches and which one squishes (even if they can'tarticulate why this happens). Where do curved mirrors lead? As students get older, they can taketheir knowledge in different directions. Understanding mirrors can lead to understanding lenses. We use curved mirrors to concentrate light, such as in telescopes and solar cookers. A curved mirror produces a transformation; therefore, it has connections to mathematics and to art. One of the most famous images of this type is M. C. Escher's Hand with Reflecting Sphere. The National Science Education Standards (1996) state that "as a result of the activities in grades K-4, all students should...[understand that] "light travels in a straight line until it strikes an object. Light can be reflected by a mirror, refracted by a lens, or absorbed by the object" (p. 127).Furthermore, students in grades 5-8 should understand that "light interacts with matter by transmission (including refraction), absorption, or scattering (including reflection). To see an object, light from that object emitted by or scattered from itmust enter the eye" (p. 155). Distributed by Key Curriculum Press, Kaleidomania is computer software that simulates reflections (andother transformations). It will let you make any kind of kaleidoscope you wantand even let you import your own pictures. The Exploratorium has lotsof small activities (they call them "snacks") about mirrors, both flat andcurved. You can build and explore corner reflectors, cylindrical mirrors(like the ones in this lab), spherical mirrors (like the Escher print, above) and even, parabolic mirrors as well as many others. Back to Fun House Mirrors