Gauge Pressure and Absolute Pressure
Absolute pressure is the total pressure at a point, while gauge pressure is the difference between absolute pressure and atmospheric pressure.
What is Gauge Pressure and Absolute Pressure?
The total pressure at a point, measured relative to a perfect vacuum.
Key formula / rule: Absolute Pressure
Key points
- Define absolute pressure and gauge pressure.
- Differentiate between absolute and gauge pressure.
- Apply the formula relating absolute, gauge, and atmospheric pressure.
- Interpret pressure readings from common devices.
Common exam trap
Confusing absolute pressure with gauge pressure.
Definitions
- Term
Absolute Pressure
- Meaning
The total pressure at a point, measured relative to a perfect vacuum.
- Term
Gauge Pressure
- Meaning
The difference between absolute pressure and atmospheric pressure.
- Term
Atmospheric Pressure
- Meaning
The pressure exerted by the weight of the atmosphere.
Learning objectives
Define absolute pressure and gauge pressure.
Differentiate between absolute and gauge pressure.
Apply the formula relating absolute, gauge, and atmospheric pressure.
Interpret pressure readings from common devices.
Formulae
- Name
Absolute Pressure
- Note
Pabs is absolute pressure, Patm is atmospheric pressure, Pgauge is gauge pressure.
- Expression
Pabs = Patm + Pgauge
- Name
Gauge Pressure
- Note
Rearrangement of the absolute pressure formula.
- Expression
Pgauge = Pabs - Patm
Prerequisites
Concept of Pressure
Atmospheric Pressure
Units of Pressure (Pascal, atm, bar)
Common mistakes
Confusing absolute pressure with gauge pressure.
Forgetting to add atmospheric pressure when calculating absolute pressure from gauge pressure.
Assuming atmospheric pressure is constant in all scenarios.
Keywords
Absolute Pressure
Gauge Pressure
Atmospheric Pressure
Fluid Statics
Pressure Measurement
Practice preview
If the atmospheric pressure is 1 atm, and the gauge pressure in a liquid is 2 atm, what is the absolute pressure at that point?…
easy
A manometer measures the pressure of a gas in a container. If the mercury level in the open arm is 20 cm higher than in the arm connected to the container, and the atmospheric pressure is 76 cm of Hg, what is the gauge p…
easy
Consider a point at a depth 'h' in a liquid of density 'ρ'. If the atmospheric pressure is P_atm, which of the following correctly represents the absolute pressure at that point?…
medium