PURPOSE: Demonstrate the wave properties of electrons.

DESCRIPTION: Electrons are emitted by the cathode at the back end of the tube, are accelerated by a high voltage and strike a target of powdered graphite crystals, producing a characteristic circular diffraction pattern. The pattern can be seen when the diffracted electrons strike a phosphorescent coating at the front end of the tube. As the accelerating voltage is increased, decreasing the wavelength of the electrons, the circles become smaller. Quantitatively, the radius of the circle can be measured to be proportional to the wavelength, which is approximately inversely proportional to the square root of the kinetic energy. The photographs below show the pattern at half voltage (left) and at full voltage (right).

SUGGESTIONS:

REFERENCES: (PIRA 7A55.30) See Demonstration Reference File for further information.

EQUIPMENT: Pre-assembled electron diffraction apparatus.

SETUP TIME: None.