What formula shows the relationship between absolute pressure and gauge pressure?

What formula shows the relationship between absolute pressure and gauge pressure?

• A. Absolute pressure = gauge pressure + atmospheric pressure
• B. Gauge pressure = absolute pressure + atmospheric pressure
• C. Absolute pressure = atmospheric pressure - gauge pressure
• D. Gauge pressure = atmospheric pressure - absolute pressure

Answer: (A)

Gauge pressure tells you how much pressure is above the surrounding atmospheric pressure, while absolute pressure is the total pressure you’d have if there were no vacuum reference—i.e., it includes the atmospheric component. So the total or absolute pressure is the atmospheric pressure plus the gauge pressure: P_abs = P_gauge + P_atm. This makes sense in practice: if the gauge reads zero, the absolute pressure equals the atmospheric pressure. If the gauge shows a positive value, you add that amount to the atmospheric baseline to get the absolute pressure. For example, at sea level (about 14.7 psi atmospheric), a gauge reading of 5 psi gives an absolute pressure of about 19.7 psi. If the gauge indicates a negative value (a slight vacuum), the absolute pressure still follows the same rule by subtracting that amount from the atmospheric pressure. The other options would invert or subtract in the wrong direction, which doesn’t align with how gauges measure relative to atmosphere.

Gauge pressure tells you how much pressure is above the surrounding atmospheric pressure, while absolute pressure is the total pressure you’d have if there were no vacuum reference—i.e., it includes the atmospheric component. So the total or absolute pressure is the atmospheric pressure plus the gauge pressure: P_abs = P_gauge + P_atm.

This makes sense in practice: if the gauge reads zero, the absolute pressure equals the atmospheric pressure. If the gauge shows a positive value, you add that amount to the atmospheric baseline to get the absolute pressure. For example, at sea level (about 14.7 psi atmospheric), a gauge reading of 5 psi gives an absolute pressure of about 19.7 psi. If the gauge indicates a negative value (a slight vacuum), the absolute pressure still follows the same rule by subtracting that amount from the atmospheric pressure.

The other options would invert or subtract in the wrong direction, which doesn’t align with how gauges measure relative to atmosphere.