Corso di Fisica Moderna

Corso di Fisica Moderna a.a. 2011/12 2nd semestre Corso di Fisica Moderna a.a. 2011/12 2nd semestre Quantum Physics grew out of Launched by experiments such as Failures of Classical Physics Which found some quantum remedies in the and Planck Hypothesis Wave-­‐parBcle duality And generated new ideas like the Uncertainty Principle and Quantum StaBsBcs Describes nature with StarBng with WavefuncBon Photoelectric effect and Blackbody radiaBon Used in Bohr Theory Led to Quantum numbers Compton ScaLering Which led to Hydrogen Energies Leading to RadiaBon curves Wien Displacement Law Schrodinger EquaBon Hydrogen Spectrum Atomic ProperBes Periodic Table And started analysis of Atomic Structure Something is WRONG Experimental facts: 1)  photo-­‐electric effect 2)  measure of the energy vs frequency spectra of an ideal oven (black body) 3)  equiparBBon of energy: inapplicable at low temperature: failure of Dulong and PeBt law 4)  Spectral structure of the atomic species Heinrich Hertz 1887 Explained by Einstein 1905 Experimental facts: 1)  photo-­‐electric effect 2)  measure of the energy vs frequency spectra of an emi`ng body. 3)  equiparBBon of energy: inapplicable at low temperature: failure of Dulong and PeBt law 4)  Spectral structure of the atomic species In 1895, at the University of Berlin, Wien and Lummer punched a small hole in the side of an otherwise completely closed oven, and began to measure the radiaBon coming out Experimental facts: 1) 
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photo-­‐electric effect measure of the energy vs frequency spectra of an ideal oven (black body) equiparBBon of energy: inapplicable at low temperature: failure of Dulong and PeBt law Spectral structure of the atomic species Experimental facts: 1) 
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photo-­‐electric effect measure of the energy vs frequency spectra of an ideal oven (black body) equiparBBon of energy: inapplicable at low temperature: failure of Dulong and PeBt law Spectral structure of the atomic species Experimental facts: 1) 
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photo-­‐electric effect measure of the energy vs frequency spectra of an ideal oven (black body) equiparBBon of energy: inapplicable at low temperature: failure of Dulong and PeBt law Spectral structure of the atomic species Hydrogen absorpBon spectra Quantum experiments ParBcle nature of light Photoelectric Effect Wave nature of electron Cavity radiaBon Davisson-­‐
Germer Experiment Blackbody radiaBon Compton ScaLering Nuclear atom Rutherford ScaLering ParBcle nature of light Discrete Atomic Spectral Lines QuanBzed atomic energy levels Franck-­‐Hertz Experiment Electron spin Stern-­‐Gerlach experiment Nature of photons: wave duality 1) 
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Thermal radiaBon: black body Coherent radiaBon Photoelectric effect: photons are quanta! Compton effect: photons behave like parBcles Experimental observaBons: 1) Stefan-­‐Boltzmann’s law Wien’s law 2) Rayleigh-­‐Jeans Planck Nature of photons: wave duality 1) 
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Thermal radiaBon: black body Coherent radiaBon Photoelectric effect: photons are quanta! Compton effect: photons behave like parBcles Ekin=hf-­‐hf0 photons 1) 
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Thermal radiaBon: black body Coherent radiaBon Photoelectric effect: photons are quanta! Compton effect: photons behave like parBcles Electrons 1)  Charge and mass: Millikan experiment 2)  ParBcle/wave character: interference and diffracBon 1)  Davisson and Germer Experiment Electrons 1)  Charge and mass: Millikan experiment 2)  Par;cle/wave character: interference and diffrac;on •  Davisson and Germer Experiment The wavelength of de Broglie wave associated with the electrons accelerated by an electric potenBal of 100 V is about 1 Å. This is almost the same as that of ordinary X-­‐rays. It is therefore supposed that, if we bombarded this electron beam on a crystal, we would observe a diffracBon paLern similar to the Laue diagram in the case of X-­‐rays. the Laue diagrams What is an atom? 1) 
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Mass and its measure Dimension Avogadro’s number Isotopes and isotopes separaBon Mass spectrometers Rutherford’s experiment Rutherford, Geiger, Marsden experiments. Hydrogen spectral lines The experiment carried out by James Franck and Gustav Ludwig Hertz in 1914 was intended to support Niels Bohr's model of the atom, according to which electrons occupy discrete energy levels that can absorb or emit energy in only certain quanBzed amounts. Grid voltage Orbital magneBsm: (cap. 12) 1)  fine structure 2)  Stern-­‐Gerlach experiment Spin-­‐Orbit interacBon Stern-­‐Gerlach’s Experiment Orbital magne;sm: Hyperfine structure Atoms in a magne;c field: 1)  Zeeman effect 2)  Anomalous Zeeman effect 3)  Paschen-­‐Back effect Atoms in an Electric field: Stark effect X-­‐ray Spectra: bremsstrahlung, absorp;on, emission Next lesson: blackbody radiaBon, Planck’s hypothesis Rutherford’s experiment Atoms in a magneBc field: 1)  Zeeman effect 2)  Anomalous Zeeman effect 3)  Paschen-­‐Back effect Experimental facts: 1)  photo-­‐electric effect 2)  measure of the energy vs frequency spectra of an emi`ng body. 3)  equiparBBon of energy: inapplicable at low temperature: failure of Dulong and PeBt law 4)  Spectral structure of the atomic species The first adequate determinaBon of the character as well as amount of solar radiaBon. S. P. Langley in 1893 at Mount Whitney in California frequency Electrons are usually used for this purpose, the radiaBon being produced in an X-­‐ray tube which contains a source of electrons and two metal electrodes. The high voltage maintained across these electrodes draws the electrons to the anode, or target, which they strike with high velocity. X-­‐rays are produced at the point of impact and radiate in all direcBons. Most of the kineBc energy of the electrons striking the target is converted into heat, less than 1% being transformed into X-­‐rays. When the rays coming from the target are analyzed, they are found to contain a mixture of different wavelengths, and the variaBon of intensity with wavelength is found to depend on the tube voltage. The intensity is zero up to a certain wavelength, called the short wavelength limit (λSWL), increases rapidly to a maximum then decreases, with no sharp limit on the long wavelength side Experimental facts: 1)  photo-­‐electric effect 2)  measure of the energy vs frequency spectra of an emi`ng body. 3)  equiparBBon of energy: inapplicable at low temperature: failure of Dulong and PeBt law 4)  Spectral structure of the atomic species The first adequate determinaBon of the character as well as amount of solar radiaBon. S. P. Langley in 1893 at Mount Whitney in California frequency Stefan-­‐Boltzmann’s law Wien’s law Le origini della Fisica QuanBsBca Crisi della fisica classica e moBvazioni per la meccanica quanBsBca Fotone: Aspe` corpuscolari della radiazione, radiazione termica, distribuzione di corpo nero , formula di Planck, derivazione di Einstein della Formula di Planck, effeLo fotoeleLrico, effeLo Compton. Aspe` ondulatori delle parBcelle Basi sperimentali della meccanica quanBsBca: interferenza, onde e parBcelle Idee chiave della meccanica quanBsBca: misura, sovrapposizione, Modern Physics began at the turn of the 20th century when Max Planck invented the idea of the quantum. The world hasn't been the same since. Albert Einstein constructed the special theory of relaBvity five years later. The nucleus was discovered and invesBgated. The states of the atom were unraveled by Niels Bohr. Light was understood to be made of waves, then parBcles, and then, with the development of Quantum Mechanics, both at the same Bme. Werner Heisenberg proposed the Uncertainty Principle, and Erwin Schrödinger thought about cats that could be alive and dead simultaneously. Einstein showed that the space-­‐Bme conBnuum is curved. origins of Quantum Mechanics; quantum structure of atoms, molecules, solids; applicaBons to lasers This course traces in some detail just how the new ideas developed. We examine the experimental and theoreBcal paradoxes that forced thinking out of the tradiBonal path