  The temperature dependence of the dielectric permittivity is taken into
account to study the energy change in a capacitor that follows a cycle between
a cold and a hot thermal reservoirs. There is a net energy gain in the process
that, in principle, can be transformed into usable work. The article is simple
enough as to be used with keen undergraduates that have taken a university
general physics or thermodynamics course. Further experimental work and a
possible technological application are suggested.
