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1、Lesson 17,25-3 Photons and the Compton Effect,In 1916 Einstein extended his photon concept:likeenergy,momentum is transferred in discrete amount.,The magnitude of the momentum p of a photon associated with a wave frequency f:,photon momentum,Photon energy E=hf,In 1923,Arthur Compton proved Einsteins
2、 view.,E=hf=mc2p=mc=hf/c,Compton s apparatus,The detector measures both the intensity of scattered x rays and their wavelengths.,The 1927 Nobel PrizeDiscovery of wavelength change in diffused x rays,Compton shift,Before collision,After collision,Conservation of momentum,Photon scattered on free elec
3、tron,Comptons interpreting in terms of energy and momentum transfers from quantum physics,Quantitatively analysis,Conservation of energy,Conservation of momentum,Compton shift,This formula indicates the increment of wavelength isindependent of scattering material but depends on thescattering angle a
4、nd increases as the scattering angle.,x component,y component,Compton wavelengthof the electron,x,(2)=,has maximum value,namely energy loss of incident photon is most;photon is scattered opposite the incident direction,electron picks up maximum kinetic energy.,Kinetic energy,Discussion,(1)=0,=,photo
5、n doesnt interact with any electrons,and through the target directly.,(3)Using a longer wavelength of light,We cannot observe the Compton effect.,(4)This effect implies:a)photon has mass,energy,and momentum;b)microcosmic particles interaction also obey energy conservation and momentum conservation.,
6、(5)Photoelectric effect and Compton effect,Photoelectriceffect,Compton effect,Incident photon,Electron,Scattered photon,Absorb photonentirely,Absorb part energyof photon,Disappear,Discussion,Checkpoint 2,Wave-particle duality of light,Light has interference,diffraction and polarization,which means l
7、ight has wavelike property.Photoelectric effect and Compton effect indicate that light has particle-like property；Photons energy,mass and momentum are:,Light has both wavelike and particle-like propertieswave-particle duality.,Summary,Example 25-3 X rays of wavelength=22 pm(photon energy=56 keV)are
8、scattered from a carbon target,and the scattering rays are detected at 45.0 to the incident beam.,(a)What is the Compton shift of the scattering rays?,Solution:,From Compton shift,=0.71 pm,(b)What percentage of the initial x-ray photon energy is transferred to an electron in such scattering?,Solutio
9、n:,The fractional energy loss(let us call it frac),for photons,25-5 Wave Nature of Matter,Physicists have finally come to the conclusion that this duality of light must be accepted as a fact of life.It is referred to as the wave-particle duality.Apparently,light is a more complex phenomenon than jus
10、t a simple wave or a simple beam of particles.,In 1923,Louis de Broglie extended the idea of the wave-particle duality.,He postulated that if light sometimes behaves like a wave and sometimes like a particle,then perhaps those things in nature thought to be particle such as electrons and other mater
11、ial objects might also have wave properties.,He suggested that p=h/might apply not only to photon but also to particles of matter.,That is,for a particle having momentum p=mv,the wavelength is given by,(de Broglie wavelength),Furthermore,in analogy with photons,E=hf,the matter waves frequency,A dust
12、 particle of mass 106 g with a speed 10 m/s,This wavelength is so small that no possible diffractionexperiment could ever detect it.Dust particles,baseball,and airplanes reveal very little of their wavelike aspects.,Electrons(me=9.11031kg)moving at a speed of 106m/s,(typical of electrons speed in at
13、oms),On the atomic scale,the wavelength of electron in the atom is of the same magnitude as interatomic spacing in matter,so by using diffraction experiment to detect the wavelength.,de Broglie wavelength:,The first figure shows electrons double-slit interference patterns and the second shows a tran
14、smission electron diffraction patterns produced from a gold foil.Similar double slits interference has been demonstrated with protons,neutrons,and various atoms.,Louis Victor de Broglie(1892 1986)Discovery of the wave nature of electrons,The 1929 Nobel Prize,Exercise.Determine the de Broglie wavelen
15、gths 1 and 2 of an electron when it is accelerated by potential differences V1=100V and V2=10000V respectively.,Solution:the electrons kinetic energy by accelerating,de Broglie wavelength,Replace by data,It has the same magnitude with x rays.Therefor,we need to use crystal observing the electron dif
16、fraction.,Exercise.A x-ray with wavelength 0.5 collides with a free electron,observing scattered x-ray in the direction of=60.Find(1)The wavelength of scattered x-ray;（2）The energy of recoil-electron.,Solution:（1）from Compton shift,Scattered x-rays wavelength,（2）from the conservation of energy,the recoil-electrons kinetic energy：,In Compton effect,electron gained maximum kinetic energy 45keV from incident x-ray.Determine the wavelength of incident photon.,Solution:,Exercise,We knew,=,electron would get maximum kinetic energy from incident x-ray,
