The Magic Mirror Illusion
Students are often fascinated by this optical illusion, which is commercially available at any science museum store or educational toy store manufactured by Francais, made in China at about $20. The illusion is formed by two concave mirrors of equal radius facing each other. The apex of the top mirror is at half of the radius from the bottom mirror and vice versa as shown in figure 1. When an object such as a small plastic toy house or a pig is hidden at the center of the bottom mirror one sees two images above near the apex of the top mirror. It is a good exercise for the students to draw the ray diagrams given the above mirror configurations. This has to be drawn with some care using rulers and protractors and applying the law of reflection. After this exercise students really gain a much deeper understanding what a normal to the plane means and how to construct images.
The answer is shown below:
