Current Reading from the Thermopile
Instead of measuring the (seebeck) voltage generated by heating one side of thermopile, we can also measure the current generated by the seebeck effect.
In the first test, a very low resistance ammeter is used (3.51 ohms). See the video clip below.
A different ammeter will give different reading to the same degree of heating of the thermopile because of the difference in resistance. A ammeter with higher resistance will cause less current.
In the second test, a higher resistance ammeter(45.3 ohms) is used to demonstrate is fact. See the video clip below.
In the third test, a even higher resistance ammeter(1782 ohms) is used.
Now we may get to understand why voltage is to measure to the temperature for thermopile, instead of getting the current generated to measure temperature. It is because of the fact that current generated will depend on the resistance of ammeter but seebeck voltage will not depend on it.
In one of the Joseph Henry Notes made by Cuyler, Theodore Ledyard (See the “classnotes” session), it said “A great quantity may be produced though its projectile force is small”. It is saying that the current can be large but the voltage is quite small, which is consistent with our modern measurement stating that magnitude of seebeck voltage is of order uV/K.
Thermoelectric cooler (also called as “Peltier Device”) is essentially a thermoelectric battery itself. A device with strong peltier effect will give strong seebeck effect as well (related by Kelvin Relation). So a Peltier device made of bismuth and antimony alloys can be used as a battery to move a motor.