To demonstrate that dissimilar metals in contact generate a voltage which varies with temperature.
Two copper wires, iron wire, beaker of ice water, beaker of hot wire on hot plate, digital voltmeter with clip leads.
A copper wire and an iron wire are wound together at one end and inserted into either boiling water or ice water. The other ends of the wires are connected to a digital voltmeter. The copper/iron thermocouple generates a voltage, but two copper wires in the same configuration will not.