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!

Homework Help: Carnot engine acting upon another Carnot engine

  1. Nov 20, 2016 #1
    1. The problem statement, all variables and given/known data
    Suppose an amount of power P_{\ell} is delivered to a load by a black box with potential difference V_T across it, driving current I through a single loop. If an amount of power P_b is applied to the black box, to sustain I at V_T, then the efficiency of this black box acting as an engine is P_{\ell}/P_b.

    Now, suppose you have exactly the same black box, exactly the same load, but an additional device (in series, so it's still a single loop) applying an emf E_{ap} and a current I. The black box may still supply power, but if E_{ap} is large enough in magnitude, the black box becomes a load. However, the black box dissipates less power when the amount of power P_b applied earlier is applied to the black box. More power P_{\ell} is delivered to the load due to the application of P_b.

    My question is: what would be the efficiency of the black box (if such a quantity exists) in its increasing P_{\ell} due to the application of P_b when it is "assisting" the applied emf E_{ap}?

    2. Relevant equations
    Energy conservation is P_{\ell} = V_T * I in the "non-assisted" case, and P_{\ell} = (E_{ap} - V_T) * I in the "assisted" case.

    3. The attempt at a solution
    I tried "guessing" an efficiency of P_{\ell} / (P_b + I * E_{ap}). If P_b is the heat flow from a temperature-difference between temperatures T_L and T_R, I ought to get something bounded between 0 and the Carnot efficiency.
  2. jcsd
  3. Nov 22, 2016 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    Are you able to explain how this problem relates to thermodynamics? Where does this problem come from?

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted