The Wave Nature of Electrons (Edexcel International A Level Physics)

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

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