UPSC Prelims 2021 · GS Paper I
Question 68: Science and Technology
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.
AnswerUPSC’s answer is (c).
A pressure cooker cooks hotter because the pressure inside rises and water then boils at a higher temperature. Steam builds up until it can lift the weighted valve on the lid and escape through the vent, so the pressure, and hence the temperature, depends on the weight of the lid or valve and the area of the hole. A heavier weight or a smaller hole gives a higher pressure. A hotter flame only makes steam faster and does not change the pressure at which it escapes.
- 1. A smaller vent lets pressure build higher before steam escapes.
- 2. A hotter flame only makes steam faster; the pressure where steam escapes stays the same.
- 3. A heavier lid or valve needs more pressure to lift, raising the boiling temperature.
How you could have got this
- If you were sure statement 2 is not correct, (a), (b) and (d) go: each of them includes 2.
What you needed to know: A hotter flame only makes steam faster; the pressure where steam escapes stays the same.
Only (c) is left. You didn’t need statements 1 or 3.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: flame temperature does not set the cooking temperature.
- (b) Wrong: flame temperature does not set it.
- (c) Right: the hole's area and the lid's weight set the pressure and the temperature.
- (d) Wrong: statement 2 is false.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2021, General Studies Paper I, Series A. The paper on upsc.gov.in.