STAGE B – Page 2

IIT Thermodynamics Illusion Questions & Trap Killers

⚠️ TRAP 1: “No Work Done” ≠ “No Energy Change”

Illusion: If W = 0, students assume ΔU = 0.

Reality:

Isochoric process → W = 0
But temperature can change
So ΔU ≠ 0

Killer Rule: ΔU depends only on ΔT.

⚠️ TRAP 2: “Adiabatic” Means No Heat, Not No Temperature Change

Adiabatic → Q = 0
Temperature still changes
Pressure & volume change together

IIT Trick: Many options wrongly say “T constant”.

⚠️ TRAP 3: Cyclic Process & Heat Confusion

Given: System returns to initial state.

ΔU = 0 always
But Q and W are NOT zero
Only net Q = net W

Trap: Options saying “no heat exchange” are wrong.

⚠️ TRAP 4: Bigger Area ≠ More Work (Sign Matters)

Clockwise PV cycle → Work positive
Anticlockwise PV cycle → Work negative

IIT Loves: Same area, opposite sign.

⚠️ TRAP 5: Entropy of System vs Universe

System entropy can decrease
Universe entropy never decreases

Golden Filter: Always ask – system or universe?

⚠️ TRAP 6: Free Expansion = Zero Work AND Zero Heat

No external pressure → W = 0
Insulated → Q = 0
Yet entropy increases

JEE Favorite: Irreversible process.

⚠️ TRAP 7: Efficiency vs Performance

Engine → Efficiency (η)
Refrigerator → COP
Heat pump → Different COP

Trap: Mixing formulas = instant zero.

⚠️ TRAP 8: Same Initial & Final State ≠ Same Heat

ΔU same
Q depends on path
W depends on path

Memory Hack: Only U is loyal.

⚠️ TRAP 9: Kelvin–Planck vs Clausius Statements

Kelvin–Planck → No 100% efficient engine
Clausius → Heat won’t flow cold → hot alone

Truth: Both are equivalent.

✅ IIT Elimination Strategy (Instant)

If violates 2nd law → Reject
If efficiency > Carnot → Reject
If entropy decreases for universe → Reject
If ignores sign convention → Reject

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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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