A level revision

Electron diffraction

Diffraction only occurs when the gap used is similar to that of the wavelength of the waves. The fact that electrons can be diffracted using a piece of graphite provides evidence that they act as waves. It also suggests their wave length is similar to that of the spaces between the atoms in the graphite.

To diffract electrons they are first accelerated before being 'shot' through a piece of graphite. The diffraction pattern that appears is the same as when light is diffracted through a circular hole.

This experiment shows how electrons act as both particles and waves:

• The diffraction pattern is the same as that for waves
• Electrons can be bent using magnets showing them to behave as charged particles

The graphite acts like a diffraction grating and so the following equation can be used to calculate the spacing between atoms (given by d):