• id: JME-09-N02
• title: Gauge vs Absolute Pressure
• tags: gauge-pressure, absolute, atmospheric

Absolute pressure = atmospheric pressure + gauge pressure. $P_{\text{abs}} = P_0 + \rho gh$. Gauge pressure = $\rho gh$ (pressure above atmospheric). A pressure gauge reads zero at atmospheric pressure. At sea level, $P_0 = 1.013 \times 10^5$ Pa = 760 mm Hg = 10.3 m of water. The fact that $P_0$ supports a 10.3 m water column explains why suction pumps cannot lift water higher than about 10 m. In JEE problems, "pressure at a point" usually means absolute pressure unless stated otherwise.