Diffraction patterns are observed when accelerated electrons in a vacuum tube interact with the spaces in a graphite crystal.
As they pass through the spaces, they diffract just like waves passing through a narrow slit and produce a diffraction pattern.
This provides evidence that electrons have wave properties.
According to wave theory, the spread of the lines in the diffraction pattern increases if the wavelength of the wave is greater.
In electron diffraction, a smaller accelerating voltage (i.e. slower electrons) gives widely spaced rings.
Increase the electron speed and the diffraction pattern circles squash together towards the middle.
This fits in with the de Broglie equation - if the velocity is higher, the wavelength is shorter and the spread of lines is smaller.
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