Authentic Classroom Explanation by IAS Monk

🍲 Q4. Physics of a Pressure Cooker

📌 Question
In a pressure cooker, the temperature at which the food is cooked depends mainly upon which of the following?

1. Area of the hole in the lid
2. Temperature of the flame
3. Weight of the lid

Select the correct answer using the code given below:

(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

✅ Correct Answer: (c) 1 and 3 only

🧑‍🏫 Authentic Classroom Explanation by IAS Monk

From first principles to final option — the UPSC way.

🔬 Concept First

Food in a pressure cooker cooks at a higher temperature because the pressure inside the cooker is increased, which raises the boiling point of water.

👉 Key principle:
Boiling point depends on pressure, not on flame temperature.

🔍 Statement-wise Analysis

Statement 1:
Area of the hole in the lid
✔️ Correct

• Steam escapes through the vent
• Smaller hole → pressure builds faster
• Pressure determines boiling point → cooking temperature

Statement 2:
Temperature of the flame
❌ Incorrect

• Flame controls rate of heating, not maximum temperature
• Once boiling begins, extra heat converts water to steam
• Temperature remains fixed at boiling point for that pressure

Statement 3:
Weight of the lid
✔️ Correct

• Heavier lid → higher pressure required to lift it
• Higher pressure → higher boiling point → faster cooking

🔍 Curiosity Raiser

Did you know?
Cooking food is actually harder on hills because lower atmospheric pressure lowers the boiling point of water, making pressure cookers essential at high altitudes.

🧠 Enrichment Notes (UPSC Lens)

• Pressure ↑ ⇒ Boiling Point ↑ ⇒ Cooking Temperature ↑
• Pressure cookers simulate lower-altitude conditions on mountains
• Same principle applies in:
  • Autoclaves
  • Industrial steam cooking
• Common UPSC Trap:
  • Equating flame temperature with cooking temperature (❌)
• Exam Value:
  • Tests understanding of thermodynamics + daily life application

🪶 IAS Monk Closing Whisper

Heat may cook the food, but pressure decides how fast.