Topics
Airplanes, Geometrical optics, Optical properties, Education

When studying the reflection and refraction of light, you might ask your students to imagine how they would use a signaling mirror if they were in a lifeboat trying to get the attention of a rescue plane. All lifeboats and rafts have signaling mirrors included among the supplies on board. But how do they work? It is not practical to just use an ordinary flat mirror because there is no way to know if you have lined up the Sun's rays with the mirror so that they intercept the plane. The basic design of a WWII-era signaling mirror (Fig. 1) features a cross pattern in the center formed by removing some of the metal that coats the back of the glass. This allows some of the sunlight to pass through the mirror and reflect off the body of the person holding the mirror. This light then reflects off...

AAPT members receive access to The Physics Teacher and the American Journal of Physics as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.