1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Thermodynamics - Heat engines

  1. Jun 9, 2016 #1
    My question is: according to Carnot cycle, the maximum efficiency of a heat engine is given by 1 - T2/T1, where T2 is the temperature of the cold source and T1 the temperature of the hot source. So, accordingly, as higher T2 is for a same T1, lowest is the efficiency of the engine. But, the other formula for efficiency (1 - Q2/Q1), gets me confuse because as bigger temperature is, minus heat is exchanged with the cold source, and as lower temperature is, more heat is exchanged with de hot source. I don't know if I missed any point but these two formulas seem contradictory for me.
  2. jcsd
  3. Jun 9, 2016 #2
    The analysis of heat engines centres around the expansion of gases. It is possible to show that the work (energy) involved in compressing or expanding gases is give by P x V ,( area under P~ V graph or ∫P.dV ).
    From the gas laws it is possible to show that P x V ∝ T.
    This means that heat energy is proportional to Absolute temp (T) and therefore the expressions Q in your equation can be replaced by T
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted