Some remarks on black hole temperature and the second law of thermodynamics

Abstract

I present a formulation of the second law of thermodynamics in the presence of black holes which makes use of the efficiency of an ideal machine extracting heat cyclically from a black hole. The Carnot coefficient is found and it is shown to be a simple function of the mass.

3 pages; part of a talk given at EFI, at the University of Chicago; misprint corrected