Question map
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.
Explanation
The correct answer is Option 3 (1 and 3 only). The boiling point of water inside a pressure cooker is determined by the internal pressure, not the intensity of the external heat source.
- Area of the hole (1): Pressure is defined as Force divided by Area (P=F/A). The size of the nozzle hole determines the area over which the steam pressure acts to lift the weight.
- Weight of the lid (3): The "whistle" or weight provides the downward force. Equilibrium is reached when the upward steam pressure equals the downward force of the weight. Higher weight or smaller hole area increases the internal pressure, thereby raising the boiling point and cooking temperature.
- Temperature of the flame (2): While a higher flame increases the rate of steam formation (speeding up the process), it does not change the maximum temperature attained. Once the required pressure is reached, the excess steam escapes, keeping the internal temperature constant at the boiling point corresponding to that pressure.
PROVENANCE & STUDY PATTERN
Full viewThis is a classic 'Applied Science' trap. It tests if you understand the *mechanism* (Physics: P = F/A) rather than just the *phenomenon*. Most aspirants fail because they confuse 'rate of heating' (flame) with 'maximum temperature achievable' (thermodynamics).
This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.
- Statement 1: Does the temperature at which food is cooked in a pressure cooker mainly depend on the area of the vent hole in the lid?
- Statement 2: Does the temperature at which food is cooked in a pressure cooker mainly depend on the temperature (heat output) of the flame or burner beneath it?
- Statement 3: Does the temperature at which food is cooked in a pressure cooker mainly depend on the weight (mass) of the lid?
- Explains that trapped steam raises internal pressure, which raises the liquid temperature.
- Attributes higher cooking temperature directly to the pressure built up inside the cooker (sealed system).
- States the higher boiling temperature inside a pressure cooker is due to increased pressure in the sealed container.
- Gives a specific example of boiling temperature (≈121°C) tied to increased internal pressure.
- Links cooking temperature and faster cooking to the increase of pressure inside the cooker.
- Emphasizes that temperature rises as pressure increases within the cooker (sealed environment).
Defines boiling point as the temperature at which a liquid boils at a given atmospheric pressure, linking phase-change temperature to pressure.
A student could use this rule plus the fact that sealed cookers raise internal pressure to infer that cooking temperature depends on internal pressure rather than vent geometry alone.
States that in a (mostly) fixed-volume vessel more air -> higher pressure and hence higher temperature (pressure–temperature relation).
Apply the gas-law idea to a pressure cooker: changing how much pressure is retained (e.g., by a vent) will change internal pressure and so cooking temperature.
Explains how ambient pressure affects volume and temperature of a gas (gas-law behaviour of a parcel under changing pressure).
Use this pattern to reason that the cooker’s internal gas behaviour (and thus temperature) will respond to pressure changes controlled by venting.
Gives a general rule that phase-change temperatures (melting point here) shift with ambient pressure.
Generalise from melting to boiling: a rise in ambient (or vessel) pressure should raise the boiling/ cooking temperature inside a cooker.
Notes that blocked air holes alter combustion and flame quality (affecting temperature delivered by the heat source).
Extend this to recognise two effects of vent area: it can influence internal cooker pressure (affecting boiling temp) and separately the stove flame/heat input (affecting cooking rate).
- States that during a phase change the system temperature does not change because supplied heat is consumed as latent heat.
- Implies that once boiling (phase change) begins, extra heat from a stronger flame goes into vaporisation rather than raising the boiling temperature.
- Gives a direct example that in a confined system an increase in pressure leads to an increase in temperature.
- Links the role of pressure to temperature in a closed container, consistent with the pressure-cooker principle that pressure controls boiling temperature.
- Explains that temperature rises because trapped steam increases pressure inside the cooker.
- Indicates the cooking temperature can exceed water's normal boiling point due to increased internal pressure.
- States the typical higher cooking temperatures achieved in pressure cookers (100–121°C), linking temperature to pressure/steam.
- Describes that steam pressure is managed and returned to ambient pressure after cooking, tying temperature to pressure control rather than lid mass.
- Specifies the lid's role is to seal the chamber and regulate (i.e., enable pressure build-up), not to set temperature by its weight.
- Implies that maintaining a seal to build pressure is the lid's function relevant to cooking temperature.
Defines mass vs weight and shows weight is a force (mass × gravity), which is the quantity that could exert extra downward force on a lid.
A student could combine this with pressure = force/area to estimate how much extra downward force from a heavier lid would change internal pressure.
Gives an example of how atmospheric pressure exerts large forces on surfaces (force over an area), illustrating that pressure arises from force applied over area.
Use the large magnitude of atmospheric pressure as a comparison to judge whether the additional force from lid weight is large enough to appreciably change cooker pressure.
Describes a sealed metal container (aneroid) whose lid moves inward/outward in response to external pressure changes — an example linking lid movement to pressure differences.
Compare how a lid responds to pressure differences in a barometer to how a pressure-cooker lid might respond to internal steam pressure versus external forces from lid weight.
States the relationship between pressure, temperature and volume (an increase in pressure can accompany an increase in temperature for gases), giving the thermodynamic link relevant to cooking temperature.
Combine with the pressure change estimated from lid weight to infer the corresponding change in steam temperature inside the cooker.
Gives the general rule that ambient pressure affects phase-change temperatures (melting point example), showing that pressure can change temperatures at which phase-related processes occur.
By analogy, a student could reason that if lid weight meaningfully raises internal pressure, the boiling/steam temperature (and thus cooking temperature) would shift accordingly.
- [THE VERDICT]: Conceptual Trap. Derived from basic Physics (NCERT Class 8/9 Force & Pressure) but applied to a household device. Not explicitly in books as a list, but inferable.
- [THE CONCEPTUAL TRIGGER]: General Science > Thermodynamics > Phase Changes. Specifically, the relationship between Pressure and Boiling Point (Gay-Lussac’s Law context).
- [THE HORIZONTAL EXPANSION]: 1. **Altitude Rule**: Boiling point drops ~1°C for every 300m ascent (water boils at ~70°C on Everest). 2. **Regelation**: Unlike most solids, Ice *melts* under pressure (why ice skating works). 3. **Impurities**: Adding salt *elevates* boiling point and *depresses* freezing point (Colligative Properties). 4. **Autoclaves**: Medical sterilizers use this exact principle (121°C at 15 psi). 5. **Latent Heat**: Steam causes worse burns than boiling water due to Latent Heat of Vaporisation (540 cal/g).
- [THE STRATEGIC METACOGNITION]: When studying a device (Microwave, Fuse, LED, Cooker), ask: 'What is the limiting factor?' Here, the whistle lifts when Internal Force > Weight. Since Force = Pressure × Area, the Pressure limit is Weight/Area. The flame only speeds up how fast you reach that limit, not the limit itself.
The temperature at which a liquid boils is set by the surrounding pressure; changing pressure changes the boiling temperature.
High-yield for questions on phase changes, cooking at altitude, and thermal processes; links physical chemistry to practical phenomena (e.g., pressure cookers). Mastering this helps answer problems about boiling-point variation with altitude or applied pressure and explain why pressurised vessels cook at higher temperatures.
- Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 7: Particulate Nature of Matter > 7.2.2 Liquid state > p. 105
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > A Parcel of Rising Air > p. 297
Pressure, temperature and volume are mutually linked such that at near-constant volume an increase in pressure is associated with an increase in temperature.
Core thermodynamic concept useful across physical geography and basic physics/chemistry questions; enables reasoning about how sealed containers, heating, or venting change internal conditions. Useful for UPSC questions that require causal chain reasoning rather than rote facts.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > Example 2: Vehicle tube > p. 296
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > A Parcel of Rising Air > p. 297
The size and openness of air holes or vents determine air supply to a flame and thus affect combustion quality and heat available for cooking.
Relevant to practical energy-use, pollution and technology questions (stoves, chimneys, cookers). Helps answer applied questions on stove efficiency, soot formation, and why vent design matters for heating even if not the main determinant of cooking temperature.
- Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Activity 4.4 > p. 70
- Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > FASCINATING FACTS > p. 97
During liquid-to-gas phase change, added heat is used as latent heat so temperature remains constant.
High-yield thermodynamics: explains why boiling-point processes have a fixed temperature during vaporisation and why heating power changes rate not temperature. Connects to cooking, heat engines, and material phase-change problems frequently tested in science and geography contexts.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > Explanation > p. 295
Raising pressure in a closed volume increases temperature, so a pressure cooker’s higher internal pressure raises the boiling point of water.
Essential for questions on gas laws, atmospheric processes and devices that use confinement (pressure cookers, tyres). Enables reasoning about how pressure changes affect thermal behaviour across geography, physics, and engineering topics.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > Example 2: Vehicle tube > p. 296
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > Adiabatic Process: Temperature Changes In A Parcel of Rising or Falling Air > p. 297
Flame characteristics (blue vs yellow/sooty) reflect combustion completeness and influence how cleanly and efficiently heat is produced.
Useful for practical-energy questions: links fuel-air mixing, appliance efficiency and heating rates. Helps explain why burner design and combustion affect time-to-cook even if final boiling temperature is set by pressure.
- Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Activity 4.4 > p. 69
Temperature of a gas in a closed/partly-closed system changes with pressure, linking cooker internal temperature to pressure conditions.
High-yield for UPSC as it connects basic thermodynamic reasoning to practical and atmospheric phenomena; helps answer questions on how changing pressure or volume affects temperature in closed systems (e.g., cookers, tyres, weather). Mastery enables analytical elimination of options in MCQs and clear explanations in mains answers.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > Example 2: Vehicle tube > p. 296
The 'Anomalous Expansion of Water'. Water is densest at 4°C, not 0°C. This allows aquatic life to survive in frozen lakes (ice floats, insulating the water below). Expect a question on why pipes burst in winter (volume increases as water freezes).
Use the 'Open Pan Analogy'. If you boil water in an open pot, does turning the gas knob to 'High' make the water hotter than 100°C? No, it just boils faster. The temperature is fixed by physics (boiling point). The same logic applies to a cooker; the temperature is fixed by the pressure valve setting. Therefore, 'Temperature of the flame' (Statement 2) cannot determine the cooking temperature. Eliminate 2 → Options A, B, and D are gone. Answer is C.
Mains GS-3 (Energy Efficiency): The pressure cooker is a prime example of 'appropriate technology' for energy conservation in rural India. It reduces fuel consumption by ~50%, directly linking to the Ujjwala Yojana (LPG adoption) and reducing indoor air pollution.