Slide 1If you want to know your progress so far, please send me an email request at [email protected] ReviewProblem: Macroscopic measurementAtomic physicsImportance of Hydrogen AtomEarly Models of the AtomExperimental testsSlide 9Problem: Rutherford’s modelSlide 11Difficulties with the Rutherford Model28.2 Emission SpectraEmission Spectrum of HydrogenAbsorption SpectraApplications of Absorption Spectrum1101/15/1901/15/19General Physics (PHY 2140)Lecture 32Lecture 32 Modern PhysicsAtomic PhysicsEarly models of the atomAtomic spectraChapter 28http://www.physics.wayne.edu/~apetrov/PHY2140/2201/15/1901/15/19If you want to know If you want to know your progressyour progress so far, please so far, please send me send me an email requestan email request at [email protected]@physics.wayne.edu3301/15/1901/15/19Lightning ReviewLightning ReviewLast lecture: 1.1.Quantum physicsQuantum physicsWave functionWave functionUncertainty relationsUncertainty relationsReview Problem: Does the process of pair production (photon → e+ e- in the vicinity of a heavy nucleus) violate conservation of mass?(1) yes(2) no(3) what mass?2hE tpD D �2hx ppD D �4401/15/1901/15/19Problem: Macroscopic measurementProblem: Macroscopic measurementA 0.50-kg block rests on the icy surface of a frozen pond, which we can assume to be frictionless. If the location of the block is measured to a precision of 0.50 cm, what speed must the block acquire because of the measurement process?5501/15/1901/15/19Atomic physicsAtomic physics6601/15/1901/15/19Importance of Hydrogen AtomImportance of Hydrogen AtomHydrogen is the simplest atomHydrogen is the simplest atomThe quantum numbers used to characterize the allowed The quantum numbers used to characterize the allowed states of hydrogen can also be used to describe states of hydrogen can also be used to describe (approximately) the allowed states of more complex (approximately) the allowed states of more complex atomsatomsThis enables us to understand the periodic tableThis enables us to understand the periodic tableThe hydrogen atom is an ideal system for performing The hydrogen atom is an ideal system for performing precise comparisons of theory and experimentprecise comparisons of theory and experimentAlso for improving our understanding of atomic structureAlso for improving our understanding of atomic structureMuch of what we know about the hydrogen atom can be Much of what we know about the hydrogen atom can be extended to other single-electron ions extended to other single-electron ions For example, HeFor example, He++ and Li and Li2+2+7701/15/1901/15/19Early Models of the AtomEarly Models of the AtomJ.J. Thomson’s modelJ.J. Thomson’s model of of the atom the atom A volume of positive chargeA volume of positive chargeElectrons embedded Electrons embedded throughout the volumethroughout the volumeA change from A change from Newton’s Newton’s modelmodel of the atom as a of the atom as a tiny, hard, indestructible tiny, hard, indestructible spheresphere“watermelon” model8801/15/1901/15/19Experimental testsExperimental testsExpect:1. Mostly small angle scattering2. No backward scattering eventsResults:1. Mostly small scattering events2. Several backward scatterings!!!9901/15/1901/15/19Early Models of the AtomEarly Models of the AtomRutherford’s modelRutherford’s modelPlanetary modelPlanetary modelBased on results of thin foil Based on results of thin foil experimentsexperimentsPositive charge is Positive charge is concentrated in the center concentrated in the center of the atom, called the of the atom, called the nucleusnucleusElectrons orbit the nucleus Electrons orbit the nucleus like planets orbit the sunlike planets orbit the sun101001/15/1901/15/19Problem: Rutherford’s modelProblem: Rutherford’s modelThe “size” of the The “size” of the atom atom in Rutherford’s model is about 1.0 × 10in Rutherford’s model is about 1.0 × 10–10–10 m. m. (a) Determine the attractive electrical force between an electron (a) Determine the attractive electrical force between an electron and a proton separated by this distance. and a proton separated by this distance. (b) Determine (in eV) the electrical potential energy of the atom.(b) Determine (in eV) the electrical potential energy of the atom.111101/15/1901/15/19The “size” of the atom in Rutherford’s model is about 1.0 × 10–10 m. (a) Determine the attractive electrical force between an electron and a proton separated by this distance. (b) Determine (in eV) the electrical potential energy of the atom.Given:r = 1.0 × 10–10 m Find:(a) F = ?(b) PE = ?Electron and proton interact via the Coulomb force( ) ( )( )29 2 2 191 2221088.99 10 1.60 101.0 102.3 10eN m C Cq qF krmN---״�= =�= �Potential energy is181 21912.3 10 14 eV1.6 10eq q eVPE k Jr J--� �= =- � =-� ��� �121201/15/1901/15/19Difficulties with the Rutherford ModelDifficulties with the Rutherford ModelAtoms emit certain discrete characteristic frequencies of Atoms emit certain discrete characteristic frequencies of electromagnetic radiationelectromagnetic radiationThe Rutherford model is unable to explain this phenomenaThe Rutherford model is unable to explain this phenomenaRutherford’s electrons are Rutherford’s electrons are undergoing a centripetal undergoing a centripetal accelerationacceleration and so should and so should radiate electromagnetic radiate electromagnetic waveswaves of the same frequency of the same frequencyThe radius should steadily decrease as this radiation is given offThe radius should steadily decrease as this radiation is given offThe electron should eventually spiral into the nucleusThe electron should eventually spiral into the nucleusIt doesn’tIt doesn’t131301/15/1901/15/1928.2 Emission Spectra28.2 Emission SpectraA gas at low pressure has a voltage applied to itA gas at low pressure has a voltage applied to itA gas emits light characteristic of the gasA gas emits light characteristic of the gasWhen the emitted light is analyzed with a spectrometer, a series of When the emitted light is analyzed with a spectrometer, a series of discrete bright lines is observeddiscrete bright lines is observedEach line has a different wavelength and colorEach line has a different wavelength and colorThis series of lines is called an This series of lines is called an emission spectrumemission