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1、Chapter 33 To 35 Quantum Physics1. Plancks Quantum Hypothesis 2. The Photoelectric Effect3. Compton Effect4. Wave Nature of Matter5. Heisenberg Uncertainty Principle6. Schrdingers Equation7. Hydrogen Atom33-1 Plancks Quantum Hypothesis (P763)Black-body Radiation:One of the observations that was unex
2、plained at the end of the 19th century was the spectrum of light emitted by hot objects.A we known that all objects emit radiation whose total intensity is proportional to the fourth power of the Kelvin temperature.The rate at which an object emits energy via electromagnetic radiation depends on the
3、 objects surface area A and the temperature T of that area in Kelvins and is given byThis is called the Stefan-Boltzmann equation, and is a universal (Stefan-Boltzmann)constantThe factor e, called the emissivity（发射率）of the objects surface, is a value between 0 and 1 that is characteristic of the mat
4、erial.A surface the maximum emissivity of 1.0 is said to be a blackbody radiator.A blackbody (绝对黑体) is a body that would absorb all the radiation falling on it (在任何温度下对任何入射辐射能都全部吸收而不反射的物体).Two important theoretical curves on blackbody based on classical idears were those proposed by W.Wien (in 1896)
5、 and by Rayleigh- Jeans (in 1900).Neither Wiens nor Rayleigh-Jeans formulations were in accord with experiment. Wiens was accurate at short wavelenths but deviated from exp. At longer ones, whereas the reverse was true for the Rayleigh-Jeans theory.A cloud covered in fair skies of physics (物理学晴 朗天空中
6、的一朵乌云)!“紫外灾难”The break came in late 1900 when Max Planck (1858-1947) proposed an empirical formula (经验式) that nicely fit the date: - Planck constant Rubens proved by experiments that it fit with experimental curve in whole wavelength region.M. Planck Germany (18581947)Planck then sought a theoredica
7、l basis for the formula by making a new and radical assumption:The energy of any molecular vibration could be only some whole number multiple of hf-quantum of energy 能量子Energy would not be a continuous quantity as had been believed for centuries; rather it is quantized it exists only in discrete amo
8、unt.h = 6.6310-34 JsPlancks Quantum Hypothesis (P765)E=n n=1,2,3. = h f“Quantum” means “discrete amount” as opposed to “continuous”.This is the first time that the quantum concept was proposed in physics history. Later, the day of December 14, 1900 was called the birthday of quantum theory.Planck go
9、t the first Nobel Physics Prize in 1918 for his radical innovation (根本的改革, 创新). 普朗克量子假设与经典理论不相容，是一个革命性 的概念，打破几百年来人们奉行的自然界连续变化 的看法，圆满地解释了热辐射现象，并成为现代量 子理论的开端，带来物理学的一次巨大变革。33-2 The Photoelectric Effect 光电效应 (P765)The photoelectric effect:1. Experimental apparatusHenrich Hertz proposed in 1887 first, th
10、e charged particles was proved as electrons later. Photoelectric effect is the phenomenon that when light shines on a metal surface, electrons are emitted from the surface.光照射某些金属时能从表面释放出电子 的效应.这时逸出的电子称为光电子.(1) The numbers of electrons in unit time emited from C proportional to the intensity of inci
11、dent light (饱和光电流与入射光强成正比). 2. Experimental results(2) Adjusting the V, there exists a stopping potential Vstop截止电压, at which the reading of meter “A” has just dropped to zero no electrons have sufficient kinetic energy to reach collector C. V-VstopThen Kmax, the maximum kinetic energy of the emitte
12、d electrons (光电子的最大初动能) can be determined using conservation of energy: Measurements show that: the maximum kinetic energy of these electrons Kmax is linearly increased with the frequency of incident light.For light of a given frequency, Kmax does not depend on the intensity of the light source (与入射
13、光强无关).(3) Varying the frequency f of the incident light and measure the associated stopping potential Vstop. The cutoff wavelength:There exist cutoff frequency f0 (红限频率,入射光频率大于f0) below which no photoelectric effect occur no matter how intense the incident light is.(4) The electrons are ejected inst
14、antaneously ( 光子打出光电子是瞬时发生的).0 = c/f0The Einsteins photoelectric equation:If the electron is to escape from the target, it must pick up energy at least equal to W0. Any additional energy (hf W0) that the electron acquires from the photon appears as kinetic energy K of the electron.Einstein summed up
15、 the experimental results as:where W0 is the work function (逸出功).电子吸收一个光子的能量 = 电子的最大初动能 + 逸出功In 19131914, carefully experiments were carried out by R.A.Millikan. The results were fully in agreement with Einsteins particle theory. If the frequency f is less than the cutoff frequency f0, where hf0 = W
16、0, no electrons will be ejected at all, no matter how great the intensity. Look at examples 33-3 to 33-5 from P767 to 768. One other aspect of the photoelectric also confirmed the photon theory. Example :Solution:Show that, for light of wavelength in nanometers, the photon energy hf in electron-volts is 1240/ For blue light, = 450nm, as the example 33-3, the energy of ph
