Last Updated: Sep 06, 2022     Views: 13026

One reason glass is chosen to make lightbulbs is because of its insulating qualities. Image: Light Bulb Tester. Parrish, Maxfield (American, 1870-1966), Designer; American Art Works Inc., Manufacturer. 1924-1934. CMoG 95.4.26

Electricity and Cold Glass

Generally, glass is a very poor conductor of electricity, at least when it is cold.

Light bulbs, x-ray tubes, and many other electrical products are made from glass. One reason glass is chosen for these products is because of its excellent electrical insulating ability. Glass, like other insulating materials, provides high resistance to the passage of electricity. This property is called volume electrical resistivity when it measures the resistance to flow of electricity throughout the body of the glass, and surface electrical resistivity when it measures the resistance of flow along the surface.

The volume resistivity of glass is approximately 10 18 (a million, million, million) time that of copper.... Conductivity, or the ability to conduct electricity, is the reciprocal of resistivity. FROM: Adams, P. Bruce, All About Glass. Corning, NY: Corning Glass Works, 1984, pp. 14.

Electricity and Hot Glass

However, the answer to your question is not that simple.  Glass conducts electricity when it is hot, but not when it is cold. 

Here is an explanation from Jane Cook, former Chief Scientist at The Corning Museum of Glass

It’s important, first to understand what temperature is, and what it means for how atoms are put together.

When we heat stuff up, we are putting energy into that stuff in the form of vibrations. In a solid, the atoms stay in one place bonded to other atoms around them. But the atoms are always vibrating, with the bonds acting like springs, as the atoms jiggle back and forth, up and down. When the temperature gets high enough, the vibrations become strong enough that the bonds can no longer hold the solid together. The solid melts and becomes a liquid.

Liquids, then, are made up of single atoms and small groups of atoms that got hot enough to move free. They still interact with each other as they move around in the liquid they’ve become. And some of the parts of the atoms that held them together in the solid – the electrons – are also free to move around more in the liquid.

Liquid soda-lime glass has enough of those electrons swimming around that, when placed in an electrical circuit, i.e., when enough voltage is applied, the electrons will move as a current through the liquid. The hotter the molten glass, the more the electrons are separated from the atoms, and the stronger the current at any voltage.

When it’s cooled back down again, the electrons are re-committed to specific atoms, and the current stops flowing.

Listen/Look Now

 

 

 

Comments (1)

  1. Borosilicate electrical field conductivity (like most materials) is initially a factor of AC frequency = an insulator at 60Hz but not so much even at only 14 kHz
    by Jim Falk on Oct 22, 2020

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