Heat Extracted and Delivered to Reservoirs in a Heat Engine

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SUMMARY

A heat engine operating between temperatures of 500K and 300K has an efficiency of 20% of the Carnot efficiency. Given that the work done per cycle is 100 kJ, the heat extracted from the hot reservoir per cycle can be calculated using the formula Qh = W / (1 - efficiency). The heat delivered to the cold reservoir can be determined by Qc = Qh - W. The discussion highlights the need for foundational knowledge in thermodynamics to solve such problems effectively.

PREREQUISITES
  • Understanding of the Carnot efficiency formula
  • Basic principles of thermodynamics
  • Familiarity with heat engine operations
  • Ability to perform calculations involving heat transfer and work
NEXT STEPS
  • Study the Carnot cycle and its efficiency calculations
  • Learn about the first and second laws of thermodynamics
  • Explore practical examples of heat engines and their performance metrics
  • Review thermodynamic textbooks or online resources for deeper insights
USEFUL FOR

Students in physics courses, particularly those studying thermodynamics, as well as educators seeking to clarify concepts related to heat engines and their efficiencies.

Willfrid Somogyi
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NO TEMPLATE---MISPLACED HOMEWORK

So it seems like a pretty simple question, and in all likelihood it is, but my lecturer somehow managed to miss this bit in his lecture notes.

A heat engine operates between 500K and 300K with 20% of the efficiency of Carnot engine operating between the same temperatures. If the work done per cycle is 100 kJ, calculate:
(i) The heat extracted from the hot reservoir per cycle.
(ii) The heat delivered to the cold reservoir per cycle

Can anyone help?
 
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For a Carnot engine operating between these temperatures, what fraction of the heat received from the hot reservoir is released to the cold reservoir? What fraction is converted to work? What is the efficiency?
 
Chestermiller said:
For a Carnot engine operating between these temperatures, what fraction of the heat received from the hot reservoir is released to the cold reservoir? What fraction is converted to work? What is the efficiency?
Sorry, to be clear this isn't homework. This is simply a practice question I found elsewhere and I'd like a complete answer if that's possible?
 
Willfrid Somogyi said:
Sorry, to be clear this isn't homework. This is simply a practice question I found elsewhere and I'd like a complete answer if that's possible?
You'd like a complete answer, but that's not how we work here at Physics Forums. We help you get the answer yourself by asking you leading questions and giving you hints. If that's not the way you are willing to proceed, then have a nice day.
 
Well it's going to be a bit of an issue as I've never been taught it, as mentioned in the original post, so I have no knowledge of any of the theory, hence why I asked for a complete answer.
 
Willfrid Somogyi said:
Well it's going to be a bit of an issue as I've never been taught it, as mentioned in the original post, so I have no knowledge of any of the theory, hence why I asked for a complete answer.
Physics Forums is not structured as a venue for providing a complete tutorial on something like this. Maybe, someday, someone will write a Physics Forums Insights article on heat engines, but, as of now, no such article exists.

Tell us more about your situation. What is the academic course that this problem comes from? If heat engines were not covered in your course, are you still expected to be responsible for the material? What textbook are you using in your course, and what other textbooks or online sources have you consulted to develop background for solving this problem?
 
Last edited:
Chestermiller said:
Physics Forums is not structured as a venue for providing a complete tutorial on something like this. Maybe, someday, someone will write a Physics Forums Insights article on heat engines, but, as of now, no such article exists.

Tell us more about your situation. What is the academic course that this problem comes from? If heat engines were not covered in your course, are you still expected to be responsible for the material? What textbook are you using in your course, and what other textbooks or online sources have you consulted to develop background for solving this problem?

It's in the syllabus and a similar question came up in a past paper, I've tried emailing my lecturer but have had no response and being out of term time he won't be available at the University itself. I'm currently on a first year Physics course. I've tried looking in the usual places including this forum, HyperPhysics and a few other online teaching resources but none offered a clear explanation. I don't have access to a textbook as the recommend ones for my course are ~ £160 and I can't afford that. The university library isn't open at the moment or I'd use the textbook there and all my peers are having the same problem as myself.
 
How do you define the efficiency of a heat engine?
 

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