Principle

Fast electrons are diffracted from a polycrystalline layer of graphite: interference rings appear on a fluorescent screen. The interplanar spacing in graphite is determined from the diameter of the rings and the accelerating voltage.

Benefits

• Experience the essence of the Nobel Prize: de Broglie (1929)
• Impressive visualization of a Nobel Prize experiment  with various changeable parameters
• Simple setup
• Easy determination of the interplanar spacing of graphite
• Perfect demonstration of wave-particle duality

Tasks

1. To measure the diameter of the two smallest diffraction rings at different anode voltages.
2. To calculate the wavelength of the electrons from the anode voltages.
3. To determine the interplanar spacing of graphite from the relationship between the radius of the diffraction rings and the wavelength.

Learning objectives

• Bragg reflection
• Debye-Scherrer method
• Lattice planes
• Graphite structure
• Material waves
• De Broglie equation