The earth radiates in the infra-red region of the spectrum. The spectrum is correctly given by

A carnot engine takes $$3 \times {10^6}$$ cal. of heat from a reservoir at $${627^ \circ }C,$$ and gives it to a sink at $${27^ \circ }C$$. The work done by the engine is

Which of the following parameters does not characterize the thermodynamic state of mattter?

''Heat cannot by itself flow from a body at lower temperature to a body at higher temperature'' is a statement or consequence of :