wave particle duality

• Wave-Particle Duality


  Concept that light and particles exhibit both wave-like and particle-like properties
• Light produces interference and diffraction patterns
• Interference and Diffraction


  • Show light as a wave
  • Can only be explained using waves interfering constructively or destructively
• De Broglie Theory


  Relates wave property (wavelength, λ) to particle property (momentum, mv)
• Planck’s constant is 6.63 × 10 –34 Js
• Probability wave


  The de Broglie wave of a particle can be interpreted as a probability wave
• Many physicists at the time weren’t very impressed with de Broglie's ideas
• Later experiments confirmed the wave nature of electrons
• Photoelectric Effect


  Shows light behaving as a particle
• Einstein explained the results of photoelectricity experiments by thinking of light as a series of particle-like photons
• Photon


  A discrete bundle of energy that can interact with an electron in a one-to-one way
• All the energy in the photon is given to one electron
• Electron Diffraction


  • Shows the wave nature of electrons
  • Diffraction patterns are observed when accelerated electrons interact with a graphite crystal
• Wavelength and diffraction pattern


  The spread of the lines in the diffraction pattern increases if the wavelength of the wave is greater
• Smaller accelerating voltage


  Gives more widely-spaced rings in electron diffraction
• Increase the electron speed


  Diffraction pattern circles squash together towards the middle
• In general, λ for electrons accelerated in a vacuum tube is about the same size as electromagnetic waves in the X-ray part of the spectrum
• If particles with a greater mass (e.g. neutrons) were travelling at the same speed as electrons, they would show a more tightly-packed diffraction pattern
• De Broglie wavelength


  λ = h / mv
• You only get diffraction if a particle interacts with an object of about the same size as its de Broglie wavelength
• A tennis ball with mass 0.058 kg and speed 100 ms–1 has a de Broglie wavelength of 10–34 m
• Particles don’t show wave-like properties all the time
• Quantum physics suggests that electrons and photons are both waves and particles at the same time
• Peer review


  The process by which other scientists evaluate a theory before it is published
• De Broglie’s theory is accepted to be true until new conflicting evidence comes along
• Only crystals with atom layer spacing around the size of the de Broglie wavelength are likely to cause the diffraction of an electron
• Wave-Particle Duality wasn’t accepted straight away
• what is a wave like nature of light ?

  diffraction
• what is a particle nature of light?


  photoelectric effect

  de-excitation and excitation
• what is de broglies equation

  lander =h/p=h/mv or wavelength=h/momentum