Lecture 30 Blackbody Radiation Vanderbilt （讲座30黑体辐射范德比尔特）.pdfVIP

Lecture 30 — Atoms and the Planck Radiation Law — March 29, 1999 Physics 221 — Lecture 30 — “Atoms and the Planck Radiation Law” March 29, 1999 Reading Meyer-Arendt Ch. 20; Hecht, Ch. 13; Young, Ch. 4. Demonstrations Planck.nb in Mathematica demonstration Problems Example 2, Ch. 20, problems 1, 2, 3, 6. Reminders See WWW for course information. 1. The end of the nineteenth century: the ultraviolet catastrophe. During the next several weeks we will be exploring quantum optics, that part of optics which is gov- erned by the laws of atoms, molecules and solids at the smallest size scales. Quan- tum electrodynamics, which underlies the phenomena of quantum optics, is perhaps the most successful theory of the twentieth century, predicting with extraordinary accuracy essentially all the properties of electrons in atoms. The origins of this the- ory lie almost a century back in time: a. Using the classical theory of the electron as an harmonic oscillator, Lorentz and others had formulated a theory of classical electrodynamics, which seemed to make perfect sense but which was seriously inconsistent with a number of experimental observations of radiation from atomic systems. b. The solution to this problem turned out to be the idea of quanta (Greek: “a little bit”) introduced by Max Planck, a professor at the Technical Univer- sity of Berlin at the end of the nineteenth century. The idea of quantization is central to our understanding of all phenomena at the atomic level. c. By the end of the nineteenth century, primitive infrared detectors were be- coming available, and physicists were starting to measure the distribution of intensity as a function of wavelength or frequency from light sources rang- ing from the sun to arc lamps (gas disch