Thermoelectric Effect: Seebeck, Peltier and the Emf Parabola

In the paper

Unit 4 carries 9 of the 50 physics marks, the largest single block in the paper; with seven chapters sharing them, this one averages a little over one (MEC publishes weights by unit, not by chapter). It is the smallest chapter in the unit and the most self-contained: two effects with a name and a date each, one parabola, and two temperatures defined off that parabola. Almost every question ever set on it is answered by the curve of thermo-emf against temperature, so learn that curve as a shape and not as a formula.

The MEC scope lines are: Seebeck and Peltier effects; Thermocouple calculations. The two headings below are those points, in MEC's order.

Three ways it is asked:

• Recall — who discovered which effect and when, which pair of metals gives the largest thermo-emf, what a thermopile is for.
• Understanding — why the Peltier effect is reversible while Joule heating is not, why a thermocouple is never used above its neutral temperature, why the neutral temperature does not move when the cold junction is warmed but the inversion temperature does.
• Application — a neutral or inversion temperature from α and β, the thermo-emf at a stated hot-junction temperature, the thermoelectric power at a stated temperature, an emf built up from the law of intermediate temperatures.