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The Kelvin-Planck statement of the second law forbids

  • A.a cycle producing work from a single heat reservoir
  • B.any transfer of heat at all from a cold body to a hotter one
  • C.any process whatever in which entropy decreases anywhere
  • D.a cycle whose thermal efficiency exceeds fifty per cent

Answer: A

Some heat must always be rejected to a colder reservoir, which is why no engine converts all its heat input to work. Heat can certainly move from cold to hot, provided work is supplied, and local entropy can fall as long as the total rises.

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