🔥 Thermodynamics – Stage 3

Page 9 : Graph-Based & Multi-Concept Problems (JEE Advanced)

In JEE Advanced, graphs test interpretation, not memory. Wrong area or wrong slope = wrong answer.

Graph Problem 1️⃣ : P–V Diagram

A gas undergoes a cyclic process shown in a P–V graph.
What does the enclosed area represent?

✔ Net work done in one cycle ✔ Clockwise → Work done by gas ✔ Anticlockwise → Work done on gas

Graph Problem 2️⃣ : T–V Graph

A straight line on T–V graph for an ideal gas.

❌ Not isothermal ❌ Not adiabatic ✔ Only equation-based path

Graph Problem 3️⃣ : P–T Graph

Straight line passing through origin in P–T graph.

✔ Constant volume process ✔ Slope ∝ number of moles

Graph Problem 4️⃣ : Area Trap

Area under P–V curve between V₁ and V₂.

✔ Represents work ❌ Area under T–V or P–T has no direct physical meaning

Multi-Concept 1️⃣ : Isothermal + First Law

Gas expands isothermally from V₁ to V₂.

✔ ΔU = 0 ✔ Q = W = nRT ln(V₂/V₁)

Multi-Concept 2️⃣ : Adiabatic Graph Slope

Compare slopes of isothermal and adiabatic curves at same point.

✔ Adiabatic curve is steeper ✔ |dP/dV|_adiabatic > |dP/dV|_isothermal

Multi-Concept 3️⃣ : Free Expansion

Gas expands into vacuum.

✔ W = 0 ✔ Q = 0 ✔ ΔU = 0 ✔ Entropy increases

Multi-Concept 4️⃣ : Heat Engine Graph

Efficiency depends on area enclosed.

✔ Larger area ≠ higher efficiency ✔ Depends on Q_in and Q_out

JEE PYQ Insight 💡

Most wrong answers come from:

Wrong graph area
Confusing slope with area
Ignoring direction of cycle

✅ Stage 3 – Page 9 Completed
➡️ Next: Stage 3 – Page 10 (JEE Advanced Mixed Integer + Conceptual Numericals)

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🔥 Thermodynamics – Objective Final Revision

Thermodynamics – Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 10
Set 11
Set 12
Set 13
Set 14
Set 15
Set 16
Set 17
Set 18
Set 19
Set 20
Set 21
Set 22
Set 23
Set 24
Set 25
Set 26
Set 27
Set 28
Set 29
Set 30
Set 31
Set 32
Set 33
Set 34
Set 35
Set 36
Set 37
Set 38
Set 39
Set 40
Set 41
Set 42
Set 43
Set 44
Set 45
Set 46
Set 47
Set 48
Set 49
Set 50
Set 51
Set 52
Set 53
Set 54
Set 55
Set 56
Set 57
Set 59

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