Physics and Chemistry Fundamentals› Basic Physics: Mechanics, Heat, Light and Waves
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.
Answer c.
The answer is (c): cooking temperature inside a pressure cooker is set by the steam pressure, which depends on the weight of the lid/valve and the area of the vent hole, not on how hot the flame is. Water boils when its saturated vapour pressure equals the pressure above it, so raising the internal pressure raises the boiling point (about 120 °C at roughly 2 atmospheres in a domestic cooker). That internal pressure is fixed mechanically: steam lifts the weight only when pressure times the hole's area exceeds the weight, so pressure equals weight divided by hole area. A hotter flame only makes steam faster, which escapes through the vent; the temperature still plateaus at the boiling point set by the pressure, so statement 2 is wrong.
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