GATE 2026 ES – Question 19
Consider: S1 Absolute pressure equals gauge pressure plus atmospheric pressure. S2 Gauge pressure uses absolute zero as datum. S3 Absolute pressure uses ambient atmospheric pressure as datum. S4 Vacuum pressure is negative pressure obtained by subtracting absolute pressure from atmospheric pressure. Which statements are correct?
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Correct answer: (C) S1 and S4
Explanation
Gauge pressure is $p_g=p_{abs}-p_{atm}$,so S1 is correct. Gauge pressure uses atmospheric pressure as datum and absolute pressure uses absolute vacuum, so S2 and S3 are false. The official key accepts **S1 and S4,C**. S4’s wording needs a sign qualification: the vacuum-pressure deficit $p_{atm}-p_{abs}$ is positive, while the corresponding gauge pressure is negative. It describes a subatmospheric condition but conflates those two sign conventions.