Physics Dept. Demonstration Manual

DEM22 - Electrical Conduction of Glass


To demonstrate that glass will conduct electricity at high temperature.

  • Glass conduction apparatus, c/w:
  • 250 watt lamp, ceramic "melting socket," line cord
  • Propane torch
  • Glass element carefully prepared and pre-tested
  • Isolation transformer


The series circuit containing the glass element and lamp bulb is open-circuited at room temperature. If the element is heated on one side to melting point, then due to the high negative resistance — temperature coefficient of glass, the conductivity increases rapidly, and at a bright red heat the I2R loss in the glass is sufficient to maintain the temperature without further use of the flame.


  1. Ensure that the A.C. switch on the conduction apparatus is on.

  2. Heat the glass element on a flat side only. Otherwise, the sagging molten glass may collapse, causing the internal conductors to short together.