Describes a thermo electric generator and mentions that the materials used should have large See beck coefficient S , small poor thermal conductivity k, and good electrical conductivity σ. Use dimensional analysis to show that Z = σS²ΔT/k is the unique dimension less figure of merit for the material for thermo electricity. Show that if the material is a metal that obeys the Wiedemann–Franz–Lorentz law then Z = (S²/L)(ΔT/T), so that the See beck coefficient is the critical parameter.