European Journal of Physics
Light rays emerge from an object in all directions. In introductory texts, three 'special' rays are selected to draw the image produced by lenses and mirrors. This presentation may suggest to students that these three rays are necessary for the formation of an image. We discuss that the three rays attain their 'special status' from the geometric solution of the equation of a hyperbola x−1 + y−1 = c−1 (mirror/lens equation). The material is suitable for use in introductory courses for science majors.
Zürcher, Ulrich, "Geometric Constructions for Image Formation by A Converging Lens" (2012). Physics Faculty Publications. 273.
This is an author-created, un-copyedited version of an article accepted for publication in European Journal of Physics. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://dx.doi.org/10.1088/0143-0807/33/5/1125