Question
Define gauge pressure.
When is gauge pressure (i) positive (ii) negative?
Give two examples where gauge pressure is more relevant.
Define gauge pressure.
When is gauge pressure (i) positive (ii) negative?
Give two examples where gauge pressure is more relevant.
✓
Answer
Definition: Gauge pressure is the pressure exerted by a fluid relative to the local atmospheric pressure.
Gauge pressure, $p_g=p-p_0$
where $\mathrm{p}$ is the absolute pressure and $\mathrm{p}_0$ is the local atmospheric pressure.
When the pressure inside a closed container or tank is greater than atmospheric pressure, the pressure reading on a pressure gauge is positive. The pressure inside a 'vacuum chamber'-a rigid chamber from which some of the air is pumped out-is less than the atmospheric pressure, so a pressure gauge on the chamber designed to measure negative pressure reads a negative value.
At a depth within a liquid of density $p_{\text {r }}$ the gauge pressure is $p_g=p-p_0=h p g$
Examples: Tyre pressure gauge, blood pressure gauge, pressure gauge on an oxygen or scuba tank.
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