The paint used on highway signs often contains small transparentspheres which provide nighttime illumination of thesigns lettering by retro-reflecting vehicle headlight beams.Consider a light ray from air incident on one such sphere ofradius r and index of refraction n. Let 6 be its incident angle,and let the ray follow the path shown in Fig. 32-66, so thatthe ray exits the sphere in the direction exactly antiparallel toits incoming direction. Consid- \ering only rays for which sin 0can be approximated as 0,determine the required valuefor n. FIGURE 32-66 86.

Chapter 30: Quantum Physics The “ideal” blackbody absorbs all the light that is incident upon it and is an ideal radiator The distribution of energy in blackbody radiation is independent of the material from which the blackbody is constructed — it depends only on the temperature, T Classical predictions were that the intensity increased rapidly with frequency, hence the ultraviolet catastrophe. Planck’s constant is a very tiny number; this means that the quantization of the energy of blackbody radiation is imperceptible in most macroscopic situations A more intense beam of light will contain more photons, but the energy of each photon does not change The photoelectric effect occurs when a beam of light strikes a metal