第36届国际物理奥林匹克竞赛实验试题及解答（英文）教案.pdfVIP

th 36 International Physics Olympiad. Salamanca (España) 2005 高中物理辅导网/ 京翰教育中心/ PLANCK’S CONSTANT IN THE LIGHT OF AN INCANDESCENT LAMP In 1900 Planck introduced the hypothesis that light is emitted by matter in the form of quanta of energy hν. In 1905 Einstein extended this idea proposing that once emitted, the energy quantum remains intact as a quantum of light (that later received the name photon). Ordinary light is composed of an enormous number of photons on each wave front. They remain masked in the wave, just as individual atoms are in bulk matter, but h – the Planck’s constant – reveals their presence. The purpose of this experiment is to measure Plancks constant. A body not only emits, it can also absorb radiation arriving from outside. Black body is the name given to a body that can absorb all radiation incident upon it, uλ T3 for any wavelength. It is a full radiator. Referring to electromagnetic radiation, black bodies absorb everything, reflect nothing, and emit everything. Real bodies are not completely black; the ratio between the energy emitted by a body and the one that T2 would be emitted by a black body at the same temperature, is called emissivity, ε, usually depending on the wavelength. T1 Planck found that the power density radiated by a body at absolute λ temperature T in the form of electromagnetic radiation of wavelength λ can be written as