Suppose you design an apparatus in which a uniformly charged disk of radius R is to produce an electric field. The field magnitude is most important along the central perpendicular axis of the disk, at a point P at distance 2.00R from the disk (Fig. 22-52a). Cost analysis suggests that you switch to a ring of the same outer radius R but with inner radius R/2.00 (Fig. 22-52b). Assume z p (a) z p (b) that the ring will have the same surface charge density as the original disk. If you switch to the ring, by what percentage will you decrease the electric field magnitude at P?

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