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Copper and Steel Thermocouple

A thermocouple made from ordinary copper and steel wire can generate enough current to deflect a compass needle. Compensating for the earth's magnetic field can make the compass sensitive enough to deflect when the thermocouple is heated with my fingers. I noticed a peculiarity in the copper and steel thermocouple while applying heat to a single junction connected to a voltmeter. For this experiment, I used a welded junction instead of a soldered one as used in the video. As I raised the temperature of the junction, the voltage reading would also increase as expected. When the temperature reached a certain point well above that of boiling water, I would observe approx 1.5 millivolts positive. But, as the temperature increased above this point, the voltage output from the junction would start to decrease until a point was reached that gave a reading of zero voltage. As the temperature increased further above this point the voltage output from the junction would start to increase again but with opposite polarity until a reading of approx 1.5 millivolts minus was read. I did not apply any more heat at this point because the junction was red hot and appeared to be near the melting point of the copper. Sparkbangbuzz.com