❄️ Thermodynamics – Stage 2

Page 8 : Refrigerator & Heat Pump (JEE Advanced)

Refrigerator & Heat Pump questions are conceptual + numerical traps in JEE Advanced. One wrong interpretation → full question gone.

1️⃣ What is a Refrigerator?

A refrigerator is a device that removes heat from a low-temperature body and rejects it to a high-temperature body by doing external work.

✔ Heat flows from cold to hot only when work is supplied.

2️⃣ Energy Flow in a Refrigerator

Heat extracted from cold body = Q₂
Work done on system = W
Heat rejected to hot body = Q₁

Energy balance:
Q₁ = Q₂ + W

3️⃣ Coefficient of Performance (COP)

COP of Refrigerator = Heat extracted / Work done

COP_R = Q₂ / W

⚠ COP is NOT efficiency
⚠ COP can be greater than 1

4️⃣ What is a Heat Pump?

A heat pump is a device that supplies heat to a hot body by extracting heat from a cold body using work.

👉 Purpose: Heating (not cooling)

5️⃣ COP of Heat Pump

COP of Heat Pump = Heat delivered / Work done

COP_HP = Q₁ / W

6️⃣ Relation Between Refrigerator & Heat Pump

Same machine → different objective

Important Relation:
COP_HP = COP_R + 1

7️⃣ Carnot Refrigerator (Ideal Case)

Maximum possible COP is given by Carnot cycle.

COP_R,max = T₂ / (T₁ − T₂)

COP_HP,max = T₁ / (T₁ − T₂)

⚠ Temperatures must be in KELVIN

8️⃣ JEE Advanced Traps

Confusing Q₁ and Q₂
Using °C instead of K
Calling COP as efficiency
Wrong sign of work

9️⃣ Ranker’s Memory Box

Refrigerator → Q₂ is useful
Heat Pump → Q₁ is useful
COP can be > 1
Always convert °C → K

✅ Stage 2 – Page 8 Completed
➡️ Next: Stage 2 – Page 9 : Carnot Engine & Absolute Temperature Scale

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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
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Set 59

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