Edexcel International A Level Physics

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2.21 The Wave Nature of Electrons

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The Wave Nature of Electrons

  • Electron diffraction was the first clear evidence that matter can behave like light and has wave properties
    • This is demonstrated using the electron diffraction tube
  • The electrons are accelerated in an electron gun to a high potential, such as 5000 V, and are then directed through a thin film of graphite
    • The lattice structure of the graphite acts like the slits in a diffraction grating
  • The electrons diffract from the gaps between carbon atoms and produce a circular pattern on a fluorescent screen made from phosphor

Electron Diffraction Experiment, downloadable AS & A Level Physics revision notes

Electrons accelerated through a high potential difference demonstrate wave-particle duality 

  • In order to observe the diffraction of electrons, they must be focused through a gap similar to their size, such as an atomic lattice
  • Graphite film is ideal for this purpose because of its crystalline structure
    • The gaps between neighbouring planes of the atoms in the crystals act as slits, allowing the electron waves to spread out and create a diffraction pattern

  • The diffraction pattern is observed on the screen as a series of concentric rings
    • This phenomenon is similar to the diffraction pattern produced when light passes through a diffraction grating
    • If the electrons acted as particles, a pattern would not be observed, instead, the particles would be distributed uniformly across the screen

  • It is observed that a larger accelerating voltage reduces the diameter of a given ring, while a lower accelerating voltage increases the diameter of the rings

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