Northwestern Physics Demos                                 Go back to Electricity   
DCS#  5D20.60NWU#  E-67Location:    ????
title: Conduction in Glass
aka:  ion mobility in molten glass.

    Two incadescent light bulbs are placed in series and plugged into 110 V AC.  One is clear and rated at 150 W to 200 W.     The other is broken, with just the glass support left behind.   When the central portion is heated to glowing, it becomes conductive and the high wattage bulb glows.  At this point, the I squared R heating is sufficient to maintain the glass in its molten state.
  What is doing the charge transfer in the glass, and why is glass at room temperature an insulator?
pix of set upset up