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Homework Help: Energy, temperatures and efficiency

  1. May 21, 2012 #1
    Hi all

    Working through a past paper as I have an exam tomorrow and can't quite see where to start with the following question.

    1. The problem statement, all variables and given/known data

    A steam engine produces 2.4 kJ of work per cycle for a heat input of 6 kJ. If the temperature of the hot source for the engine is 600 °C and the temperature of the cold sink is 100°C, what is the maximum possible efficiency of the engine?

    2. Relevant equations

    The only equations I can think of relating to this question involve other variables that aren't given. My initial thought was that as we're finding the efficiency any unknown values will cancel each other out, but I don't seem to get anywhere.

    Could somebody please point me in the direction of what equation I should be looking at?

    The annoying thing is it's only a 2 mark question!

    Thanks in advance.
  2. jcsd
  3. May 21, 2012 #2


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    Homework Helper

    They are asking for the maximum efficiency, for a heat engine, this is also called the Carnot efficiency. This efficiency can be expressed with what you are given. Check wikipedia for the formula (it only depends on the temperatures of the hot and cold reservoirs) :) .
  4. May 21, 2012 #3
    Thanks a lot for that. I guess I missed the lecture on it :p

    Thanks for replying as well.
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