Thermocouple and thermopile, both make electricity from heat.

Thermocouple and thermopile, both make electricity from heat. A thermocouple is formed when two dissimilar metals are joined at two endpoints. A small voltage is produced when the two endpoints are at different temperatures. (For small temperature changes, the voltage is roughly proportional to the temperature difference of the endpoints.) This demo has both a thermocouple made of iron and copper wires, and a thermopile. The thermopile is a device made up of many thermocouples in series so that the voltage produced is much larger than with a single thermocouple. The reflective horn focuses infrared radiation (heat) onto the thermopile. The iron-copper thermocouple should respond favorably to heat from the fingers, and strongly to the heat of a match. The horn thermopile should respond strongly to the hand at a distance of one foot.