Spark image

Electron diffraction

The very small wavelength of electrons means that the obstacles used to diffract them must also be very small such as the atomic lattice. Electrons are accelerated in an electron gun to a potential of 4000 V and fall on a thin sheet of graphite. The electrons diffract from the carbon atoms giving a circular pattern on the screen.

The diffraction pattern observed on the screen is a series of concentric rings.

Wavelength of an electron (l) = h/p     p is the momentum of the electron

A larger accelerating voltage reduces the diameter of a given ring.

Wavelength of an electron (l) accelerated through a p.d of V volts = 12.27x10-10/V1/2

© Keith Gibbs 2010