Chapter 11.pdf

11.1MirrorsHere is a summary of what youwill learn in this section:• The angle of incidence equalsthe angle of reflection.• Plane mirrors produce a virtualimage that is upright andlocated as far behind the mirroras the reflected object is infront of it.• Concave mirrors produce anenlarged, upright, virtual imageif the object is closer to themirror than the focal point.• Concave mirrors produce aninverted, real image if theobject is farther away from themirror than the focal point.• Convex mirrors produce anupright, virtual image that issmaller than the object.Figure 11.1 The stainless steel mirror above Viganella is controlled by computer to follow thepath of the Sun.Figure 11.2 The construction of the mirrorBrightening a Winter’s DaySummer in the Italian village of Viganella high in theItalian Alps is peaceful, warm, and above all — sunny.But winter is another story. As the hours of daylightshrink each autumn and the Sun spends less and less timeabove the horizon each passing day, Viganella loses itsdirect view of the Sun. Viganella is located at the bottomof a steep valley, and every winter the mountains blockout the Sun’s rays from November 11 to February 2.During this time, the village is completely in themountain’s shadow.But thanks to the science of optics, that situation hasnow changed. In 2006, a large flat mirror was placed atthe top of one of the nearby mountains and directed at thevillage square (Figure 11.1). Airlifted into position with ahelicopter at a total cost of about $170 000, the 5 m 8 mrectangular sheet of stainless steel is perched high aboveViganella (Figure 11.2).416 UNIT D Light and Geometric Optics