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GL028 - Conduction through hot glass
You can demonstrate that hot glass is an electrical conductor (hot glass is actually an example of a solid electrolyte). This is counterintuitive because at room temperature, glass is a good electrical insulator. The resistivity of glass decreases as it becomes hot. You can demonstrate the conduction by applying a voltage across the glass rod, say 12 V, and putting a 0 – 10 mA ammeter in the circuit. It is more impressive and memorable to put a lamp in series with the glass rod so that it lights up when the glass conducts. The difficulty is that even at high temperatures, the conductivity of hot glass is orders of magnitude less than metal.

Please note this replaces SRA023 - Conduction through hot glass