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Thermodynamics and engines
This option topic links energy transfer to heat engines.
0
Objectives
10
Flashcards
10
Questions
90 min
Study time
AqaA LevelPhysicsEngineering physics
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Syllabus checklist
What you need to know
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First law of thermodynamics4 objectives
- State the first law of thermodynamics.
- Distinguish heat supplied, work done and internal energy change.
- Apply sign conventions consistently.
- Analyse energy transfers in thermodynamic processes.
Non-flow processes4 objectives
- Describe common non-flow thermodynamic processes.
- Apply gas laws to idealised processes.
- Explain energy transfer in isothermal and adiabatic contexts.
- Interpret process changes on p-V diagrams.
The p-V diagram4 objectives
- Interpret p-V diagrams for gas processes.
- Calculate work done from area under or within p-V graphs.
- Relate p-V cycle area to net work output.
- Distinguish expansion work from compression work.
Engine cycles4 objectives
- Describe a heat engine cycle using p-V diagrams.
- Calculate efficiency from energy input and useful work output.
- Explain energy losses in real engines.
- Compare ideal and practical engine cycles.
Second Law and engines4 objectives
- State the Second Law qualitatively for heat engines.
- Explain why no heat engine is perfectly efficient.
- Discuss heat sinks and waste energy.
- Link engine limits to thermodynamic reasoning.
Reversed heat engines4 objectives
- Describe the operation of a reversed heat engine.
- Compare refrigerators and heat pumps.
- Use coefficient of performance where appropriate.
- Explain energy transfers in cooling and heating systems.
Key terms
First Law of ThermodynamicsInternal Energyheat suppliedwork doneSign ConventionsEnergy TransferNon-flow ProcessIsothermal ProcessAdiabatic Processp-V diagram
Exam tips
- Understanding the First Law of Thermodynamics: Remember that the first law of thermodynamics states that the change in internal energy of a system is equal to the heat supplied to the system minus the work done by the system.
- Apply energy transfer in First law of thermodynamics: Identify the energy transfer first, then connect it to Distinguish heat supplied, work done and internal energy change. using a named engineering system and the correct physical quantity.
Common mistakes
- Misunderstanding the First Law of Thermodynamics: To clarify, state the first law of thermodynamics as ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system. Ensure to apply the correct sign conventions for heat and work. For example, if 500 J of heat is added to a system and 200 J of work is done by the system, the change in internal energy is calculated as follows: ΔU = 500 J - 200 J = 300 J. Thus, the internal energy increases by 300 J.
- Distinguishing Heat Supplied and Work Done: Heat supplied refers to energy transferred due to temperature difference, while work done is energy transferred when a force acts through a distance. Heat is relevant in processes like heating a gas, while work is relevant in processes like compressing a gas. Understanding this distinction is crucial for analyzing thermodynamic processes accurately.
Practice preview
- What does the first law of thermodynamics state?
- In the context of the first law of thermodynamics, which of the following correctly distinguishes between heat supplied, work done, and internal energy change?
- Which of the following statements correctly applies sign conventions in thermodynamics?
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