MHT-CET Physics · Teaching notes
Thermodynamics — MHT-CET Physics
Thermodynamics has 84 past-year questions in the MHT-CET bank, about one in five HARD. One law carries the chapter: the heat given to a gas goes into its internal energy and the work it does, Q = ΔU + W. Which process the gas follows decides how the heat splits, and the adiabatic relations PV^γ = constant and TV^(γ−1) = constant carry most of the HARD questions. A short last page turns the same ideas into the efficiency of a Carnot engine. Every PYQ is tagged.
Every subtopic, worked example, formula and trap in one printable document — answers shown, ready to share.
Subtopic notes
The First Law of Thermodynamics
37 PYQsHeat Q given to a gas is shared between the rise in its internal energy ΔU and the work W it does on its surroundings, Q = ΔU + W; internal energy depends only on the state, so ΔU is the same along any path and zero round a cycle.
The Four Processes and the Adiabatic Relations
36 PYQsHolding temperature, heat, pressure or volume fixed gives the isothermal, adiabatic, isobaric and isochoric processes; an adiabatic change of an ideal gas follows PV^γ = constant, equivalently TV^(γ−1) = constant, which is steeper on a P–V graph than an isothermal.
The Carnot Engine and the Refrigerator
11 PYQsA Carnot engine runs between a hot source at T₁ and a cold sink at T₂ through two isothermal and two adiabatic steps, and its efficiency 1 − T₂/T₁ is the most any engine between those temperatures can reach; run backwards it is a refrigerator with coefficient of performance T₂/(T₁ − T₂).
Formula & revision sheet
7 formulas · 12 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
7 formulas · 12 gotchas across all subtopics — the exam-eve cheat-sheet
Formulas (3)
Watch out for (5)
- Getting the sign of work wrong→ Q = ΔU + W and its Signs
- Reading the direction of a cycle→ Q = ΔU + W and its Signs
- Inverting the ratio→ How Heat Splits at Constant Pressure
- Using C_v for heat at constant pressure→ How Heat Splits at Constant Pressure
- Dividing by γ instead of γ − 1→ Work in an Adiabatic Change
Formulas (3)
Watch out for (5)
- Calling the steeper curve isothermal→ Recognising Each Process
- Thinking an adiabatic keeps temperature constant→ Recognising Each Process
- Using γ in the temperature relation→ The Adiabatic Relations
- Forgetting that 'sudden' means adiabatic→ The Adiabatic Relations
- Applying one rule to the whole chain→ Chaining and Comparing Processes
Watch out for (2)
- Using degrees Celsius in the efficiency→ Efficiency and Coefficient of Performance
- Changing the source when the sink moves→ Efficiency and Coefficient of Performance
PYQ weightage by concept
7 concepts · 84 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
7 concepts · 84 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Q = ΔU + W and its Signs | 17 | 20% |
| How Heat Splits at Constant Pressure | 17 | 20% |
| Work in an Adiabatic Change | 3 | 4% |
| Concept | PYQs | Share |
|---|---|---|
| The Adiabatic Relations | 16 | 19% |
| Recognising Each Process | 13 | 15% |
| Chaining and Comparing Processes | 7 | 8% |
| Concept | PYQs | Share |
|---|---|---|
| Efficiency and Coefficient of Performance | 11 | 13% |
Test yourself on Thermodynamics
20 past MHT-CET questions from this chapter, timed at 18 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.