The difference between gauge pressure and absolute pressure is the atmospheric pressure at sea level (14.7 psi).

The difference between gauge pressure and absolute pressure is the atmospheric pressure at sea level (14.7 psi).

• A. True
• B. False
• C. Not determinable
• D. Both are the same

Answer: (D)

The key idea is that gauge pressure and absolute pressure differ by the amount of atmospheric pressure. Gauge pressure is what you read with a typical gauge: it shows how much pressure exists above the surrounding atmospheric pressure. Absolute pressure is the total pressure measured from a perfect vacuum, so it includes that atmospheric component. In formula form: P_absolute = P_gauge + P_atm. Therefore, the difference between the two is exactly the atmospheric pressure, not a fixed value. At sea level under standard conditions, P_atm is about 14.7 psi, so the difference would be around 14.7 psi in that ideal case. But atmospheric pressure varies with altitude and weather, so the exact difference isn’t always 14.7 psi. So gauge and absolute pressures are not the same; the difference between them is the local atmospheric pressure.

The key idea is that gauge pressure and absolute pressure differ by the amount of atmospheric pressure. Gauge pressure is what you read with a typical gauge: it shows how much pressure exists above the surrounding atmospheric pressure. Absolute pressure is the total pressure measured from a perfect vacuum, so it includes that atmospheric component.

In formula form: P_absolute = P_gauge + P_atm. Therefore, the difference between the two is exactly the atmospheric pressure, not a fixed value. At sea level under standard conditions, P_atm is about 14.7 psi, so the difference would be around 14.7 psi in that ideal case. But atmospheric pressure varies with altitude and weather, so the exact difference isn’t always 14.7 psi.

So gauge and absolute pressures are not the same; the difference between them is the local atmospheric pressure.