If you want to know your progress so far, please send me an email request [email protected] ReviewReview problem: photoeffect27.4 X-RaysProduction of X-raysProduction of X-raysDiffraction of X-rays by CrystalsSchematic for X-ray DiffractionPhoto of X-ray Diffraction PatternBragg’s LawProblem: X-ray diffraction27.4 The Compton EffectCompton ScatteringCompton ScatteringProblem: Compton scatteringAn x-ray photon is scattered by an electron. The frequency of the scattered photon relative to that of the incident photon (aA photon of energy E0 strikes a free electron, with the scattered photon of energy E moving in the direction opposite that of27.8 Photons and Electromagnetic Waves28.9 Wave Properties of ParticlesThe Davisson-Germer ExperimentA non-relativistic electron and a non-relativistic proton are moving and have the same de Broglie wavelength. Which of the foIf you want to know your progress so far, please send me an email request [email protected]/11/200311/11/2003General Physics (PHY 2140)Lecture 28Lecture 28¾ Modern Physics9Quantum Physics9Compton scatteringChapter 27http://www.physics.wayne.edu/~apetrov/PHY2140/2211/11/200311/11/2003If you want to know If you want to know your progressyour progressso far, please so far, please send me send me an email requestan email [email protected]@physics.wayne.edu3311/11/200311/11/2003Lightning ReviewLightning ReviewLast lecture:1.1.Quantum physicsQuantum physics99Photoeffect, 1, 2,3,...nEnhf n==PhotoeffectKE hf=−ΦReview Problem: A xenon arc lamp is covered with an interference filter that only transmits light of 400- nm wavelength. When the transmitted light strikes a metal surface, a stream of electrons emerges from the metal. If the intensity ofthe light striking the surface is doubled,1. more electrons are emitted in a given time interval.2. the electrons that are emitted are more energetic.3. both of the above.4. neither of the above.4411/11/200311/11/2003Review problem: photoeffectReview problem: photoeffectMolybdenum has a work function of 4.20 eV. Calculate the stoppinMolybdenum has a work function of 4.20 eV. Calculate the stopping g potential if the incident light has a wavelength of 180 nm.potential if the incident light has a wavelength of 180 nm.5511/11/200311/11/2003Molybdenum has a work function of 4.20 eV. Calculate the stoppinMolybdenum has a work function of 4.20 eV. Calculate the stopping potential if the g potential if the incident light has a wavelength of 180 nm.incident light has a wavelength of 180 nm.Recall that KEKEmaxmax==hfhf--ΦΦ. This can be used to obtain kinetic energy, which will be equal to electric potential energy Given:Φ = 4.40 eVλ = 180 nmFind:Vs= ?()maxsKE e V=∆shf hcVeee eλΦΦ∆=−=−Thus, Or numerically,()()()( )()()34 891919196.63 10 3.00 10180 10 1.60 104.20 1.60 102.711.60 10sJs msVmCeV J eVVC−−−−−×⋅ ×∆=×××−=×6611/11/200311/11/200327.4 X27.4 X--RaysRaysElectromagnetic radiation with short wavelengthsElectromagnetic radiation with short wavelengthsWavelengths less than for ultravioletWavelengths less than for ultravioletWavelengths are typically about 0.1 nmWavelengths are typically about 0.1 nmXX--rays have the ability to penetrate most materials with relative rays have the ability to penetrate most materials with relative easeeaseDiscovered and named by Roentgen in 1895Discovered and named by Roentgen in 18957711/11/200311/11/2003Production of XProduction of X--raysraysXX--rays are produced when highrays are produced when high--speed electrons are suddenly speed electrons are suddenly slowed downslowed downCan be caused by the electron Can be caused by the electron striking a metal targetstriking a metal targetA current in the filament causes A current in the filament causes electrons to be electrons to be emittedemittedThese freed electrons are These freed electrons are accelerated toward a dense accelerated toward a dense metal targetmetal targetThe target is held at a higher The target is held at a higher potential than the filamentpotential than the filament8811/11/200311/11/2003Production of XProduction of X--raysraysAn electron passes near a An electron passes near a target nucleustarget nucleusThe electron is deflected from The electron is deflected from its path by its attraction to the its path by its attraction to the nucleusnucleusThis produces an accelerationThis produces an accelerationIt will emit electromagnetic It will emit electromagnetic radiation radiation when it is acceleratedwhen it is acceleratedThe maximum x-ray energy, and minimum wavelength results when the electron loses all its energy in a single collision, such thate∆V= hfmax= hc/λminor therefore minhceVλ=∆9911/11/200311/11/2003Diffraction of XDiffraction of X--rays by Crystalsrays by CrystalsFor diffraction to occur, the spacing between the lines For diffraction to occur, the spacing between the lines must be approximately equal to the wavelength of the must be approximately equal to the wavelength of the radiation to be measuredradiation to be measuredFor XFor X--rays, rays, the regular array of atoms in a crystal can act the regular array of atoms in a crystal can act as a threeas a three--dimensional grating for diffracting Xdimensional grating for diffracting X--raysrays101011/11/200311/11/2003Schematic for XSchematic for X--ray Diffractionray DiffractionA continuous beam of XA continuous beam of X--rays rays is incident on the crystalis incident on the crystalThe diffracted radiation is very The diffracted radiation is very intense in certain directionsintense in certain directionsThese directions correspond These directions correspond to constructive interference to constructive interference from waves reflected from the from waves reflected from the layers of the crystallayers of the crystalThe diffraction pattern is The diffraction pattern is detected by photographic filmdetected by photographic film111111/11/200311/11/2003Photo of XPhoto of X--ray Diffraction Patternray Diffraction PatternThe array of spots is called a The array of spots is called a LaueLauepatternpatternThe crystal structure is The crystal structure is determined by analyzing the determined by analyzing the positions and intensities of the positions and intensities of the various spotsvarious spotsThis is for NaClThis is for NaCl121211/11/200311/11/2003Bragg’s LawBragg’s LawThe beam