User:Jared A. Booth/Notebook/Physics 307L/2009/10/12

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Electron Diffraction


1) To demonstrate the wave properties of electrons.
2) Examine the de Broglie relation \lambda = \frac {h}{p}
3) To measure the diffraction planes of graphite.


In 1924 Lois de Broglie proposed that as photons can be seen as both waves and particles, so too can electrons.
Specifically, he postulated that the wavelength of ALL particles was related to their respective momenta by what is
now known as the de Broglie relation. A direct consequence of this relation is the prediction of interference
patterns similar to those produced by photons passing through narrow slits. As a result of this prediction, a
simple proof for the wave nature of matter can be constructed to demonstrate this interference pattern. Perhaps
the most difficult obstacle in designing this experiment is in finding a diffraction grating with the appropriate
spacing to produce the desired interference.


  • Tel 2501 Universal stand
  • Electron Diffractor 2555 (5Kv .3mA)
  • Teltron Limited London England 813 KV Power Unit
  • HP 6216B Power Supply
  • Wavetek Meterman 85XT multimeter
  • Carrera Precision 6" digital caliper alloy. Note: the digital caliper's battery was low, so it was used as a standard caliper instead.


  1. The main safety concern during this procedure is electrical shock as high voltages(813KeV power supply) will be used. Standard high voltage safety precautions should be taken, including checking all equipment for damage and ensuring the equipment is properly connected.
  2. The second concern is the integrity of the equipment. Most importantly, the graphite diffraction tube. As indicated in the lab manual, the graphite is extremely thin and can be easily punctured by current overload. Use the multimeter to ensure the current stays below the maximum allowed current (0.25mA). Additionally, check the target regularly during the experiment for a red glow, indicative of current overload.


The procedure should be followed from the Lab Manual experiment 3, electron diffraction.

The following circuit was set up, with the following modification: The low voltage bias was inverted; a multimeter was put in series between the positive HV source and plug G7 on the mount to measure current. NOTE: the max voltage measurable by the multimeter is 1000V. It is important to only measure current with the multimeter while it is connected to prevent damage to the instrument as up to 5kV will be used in this experiment.
Image taken from here

Raw Data

Voltage (kV) Inner Radius (mm) Inner Diameter (mm) Outer Radius (mm) Outer Diameter (mm)
4.8 n/a 22.5 n/a 41.75
4.77 12.5 n/a 20.0 n/a
4.70 12.0 22.75 20.5 41.5
4.60 12.5 23.5 21.5 42.1
4.50 13.0 23.75 21.75 42.5
4.40 12.75 25.0 21.25 42.5
4.30 12.25 24.0 21.1 43.0
4.20 12.5 25.25 21.5 42.5
4.10 12.75 24.7 21.25 43.1
4.00 14.2 24.3 23.25 44.5
3.75 13.0 25.75 23.5 46.0
3.50 14.0 27.0 23.0 48.5
3.25 14.0 27.7 24.0 51.1
3.00 14.5 28.5 25.0 53.1
2.75 15.0 31.8 25.5 54.25
2.50 n/a n/a n/a n/a





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