Physics Dept. Demonstration Manual

DEM22 - Electrical Conduction of Glass

Objective:

To demonstrate that glass will conduct electricity at high temperature.

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


Method:

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.

Note:

  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.