Question 68 from UPSC CSE 2021 - Basic Science

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.

Accepted Answer

Correct Option: C. 1 and 3 only

Strategy: Focus on the mechanisms that directly regulate internal pressure.
- The area of the steam vent hole controls steam release.
- The weight on the vent/valve determines the pressure threshold for steam to escape.
- The external flame's temperature only affects the rate at which pressure is reached, not the maximum pressure or temperature.

Key Info: A pressure cooker operates by trapping steam to raise internal pressure, which in turn increases the boiling point of water and allows for faster cooking at higher temperatures.

**How Pressure is Regulated**
- **Steam Vent Area:** The size of the vent hole controls steam release. A smaller hole allows pressure to build up more, leading to higher internal temperatures, while a larger hole results in lower pressure.
- **Lid Weight:** The weight on the pressure regulator (valve or whistle) sets the maximum pressure. Steam only escapes once the internal pressure overcomes this weight.

**Role of External Factors**
- **Flame Temperature:** The heat source's temperature affects only how quickly the cooker reaches its target pressure. Once the set pressure is achieved, excess steam escapes, and the internal temperature does not increase further with more heat.
- **Altitude:** At higher altitudes, atmospheric pressure is lower, causing water to boil at a lower temperature. A pressure cooker compensates for this by creating a controlled high-pressure environment, raising the cooking temperature back to an effective level.

**Underlying Physics Principle**
The core principle is that the boiling point of a liquid increases with pressure, a relationship described by the Clausius-Clapeyron equation. Therefore, the cooking temperature is determined by the pressure, which is controlled by the vent and lid weight, not the external flame.

Answer

Option A: 1 and 2 only

Answer

Option B: 2 and 3 only

Answer

Option D: 1, 2, and 3

In a pressure cooker, the temperature at which the food is cooked depends mainly upon which of the following? Area of the hole in the lid Temperature of the flame Weight of the lid Select the correct answer using the code given below.

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

Area of the hole in the lid

Temperature of the flame

Weight of the lid
Select the correct answer using the code given below.