🔥 Thermodynamics – Stage 3

Page 6 : Multi-Concept PYQs (Hidden Trap Edition)

These questions combine 2–3 concepts and test thinking speed under pressure.

PYQ 1️⃣ : Isochoric + Isothermal Combo

A gas is heated at constant volume, then allowed to expand isothermally to original pressure.

Logic:
Step-1 (Isochoric): W = 0, Q = ΔU
Step-2 (Isothermal): ΔU = 0, Q = W

❌ Treating entire process as isothermal

PYQ 2️⃣ : Cyclic Process Energy Trap

Gas undergoes a closed cycle with net work done.

ΔU = 0 ⇒ Q_net = W_net

❌ Assuming zero heat because cycle ends at same state

PYQ 3️⃣ : Free Expansion + Ideal Gas

Ideal gas expands freely in vacuum.

Q = 0, W = 0 ⇒ ΔU = 0 ⇒ T constant

❌ Thinking expansion always causes cooling

PYQ 4️⃣ : Entropy + Reversibility

Two identical bodies at different temperatures exchange heat.

ΔS_total > 0 ⇒ Irreversible

❌ Forgetting total entropy, checking only system

PYQ 5️⃣ : PV Graph + Thermodynamics

Straight line on P-V graph from (P₁,V₁) to (P₂,V₂).

Work = area under curve (Trapezium)

❌ Using W = PΔV blindly

PYQ 6️⃣ : Adiabatic Temperature Trap

Rapid expansion of gas in insulated cylinder.

Q = 0 ⇒ ΔU = −W ⇒ Temperature decreases

❌ Assuming insulation means constant temperature

PYQ 7️⃣ : Heat Engine Logic Test

Engine absorbs Q₁, rejects Q₂.

Efficiency = 1 − Q₂/Q₁

❌ Using Carnot formula without temperature data

PYQ 8️⃣ : Degrees of Freedom Trap

Same heat supplied to monoatomic and diatomic gas.

ΔT ∝ 1/f

❌ Assuming equal temperature rise

PYQ 9️⃣ : Entropy Zero Fallacy

Reversible adiabatic process.

ΔS = 0 (only here!)

❌ Extending this to irreversible adiabatic

PYQ 🔟 : Final State Deception

Same initial & final states ≠ same work/heat

✅ Stage 3 – Page 6 Completed
➡️ Next: Stage 3 – Page 7 (Full JEE Advanced Mixed PYQ Drill)

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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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