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GATE 2020 ME (ME2) – Question 25

Fluid Mechanics · Fluid properties, fluid statics, forces on submerged bodies, stability of floating bodies · 1 mark · Multiple choice

In the space above the mercury column of a barometer tube, the gauge pressure of vapour is ______.

  1. positive, but more than one atmosphere
  2. negative
  3. zero
  4. positive, but less than one atmosphere

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Show answer and explanation

Correct answer: (B) negative

Explanation

The space above the column is near vacuum with only low mercury vapour pressure. Gauge pressure equals absolute pressure minus atmospheric pressure, so it is **negative,B**. Small positive absolute vapour pressure does not imply positive gauge pressure.