What is the Thermal Efficiency of an Engine?

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Homework Help Overview

The discussion revolves around determining the thermal efficiency of an engine, with reference to a specific problem involving a thermodynamic cycle illustrated in a provided image. The subject area includes concepts from thermodynamics, particularly focusing on processes such as isobaric, isochoric, and adiabatic processes.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the need to substitute relevant equations to find the heat values Qc and Qh. There are questions about the constants during different thermodynamic processes and what information is missing at specific points in the cycle. Some participants express uncertainty about how to derive the necessary values from the provided graph.

Discussion Status

There is an ongoing exploration of the problem, with participants sharing their understanding of the processes involved and questioning what specific data is needed to proceed. Some have provided rough work to illustrate their attempts, while others emphasize the importance of making an initial attempt before seeking further assistance.

Contextual Notes

Participants note a perceived lack of information regarding the three points in the thermodynamic cycle, which may hinder their ability to solve the problem effectively. There is also a mention of homework rules that encourage individual attempts before seeking help.

yecko
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Homework Statement


http://i.imgur.com/SQ6jx94.png
SQ6jx94.png

(sorry for the low resolution~ it's already the best i can make it~)

Homework Equations


U=Q+W
the three variables of isobaric, isochoric, adiabatic process (can i save my effort from typing all of them out?)
e=(Qh-Qc)/Qh

The Attempt at a Solution


Substitute the relevant equations in order to get Qc & Qh
it always seems a lack of information to the three points
there should be a specific route for substituting the variables to the cycle and the few thought by me should be wrong
can anyone tell me the right way to get option "e" here?

Thank you
 
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Show your working.

yecko said:
it always seems a lack of information to the three points

I haven't attempted a solution but usually these come from the data provided on the graph combined with your knowledge about what is constant during an isobaric, isochoric, or adiabatic process.
 
CWatters said:
what is constant during an isobaric, isochoric, or adiabatic process.
isobaric=>p constant
isochoric=>v constant
adiabatic=>q constant
 
So of P, V, and T which are you missing at each of the three points and how might you work them out from the info provided?
 
yecko said:
isobaric=>p constant
isochoric=>v constant
adiabatic=>q constant
You must attempt the question yourself. Get as far as you can and then post that attempt here so that the homework helpers can see where your misunderstanding comes in.
 

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