FAA Aviation Mechanic General (AMG)Physics, Math and Fluid LinesMedium
A confined gas in a rigid, sealed hydraulic accumulator has a pressure of 50 psia at a temperature of 60°F. If the container cannot expand and the gas is heated to 160°F, what is the new pressure (assume constant volume)?
- A59.6 psia
- B67.3 psia
- C45.2 psia
- D50.0 psia
Show answer & explanationAnswer & explanation
Correct answer: A. 59.6 psia
This is Gay-Lussac's Law: P1/T1 = P2/T2, using absolute temperature in Rankine (°F + 460). T1 = 520°R, T2 = 620°R. P2 = 50 × (620/520) = 59.6 psia.
Why the other options are wrong
- B. This value results from using Fahrenheit temperatures directly instead of Rankine.
- C. This results from dividing instead of multiplying the temperature ratio.
- D. This ignores the temperature change entirely, assuming constant pressure.
Gay-Lussac's Law
For a fixed volume of gas, pressure is directly proportional to absolute temperature: P1/T1 = P2/T2.
- Volume must remain constant
- Temperature must be converted to absolute scale (Rankine or Kelvin)
- Used to predict pressure changes in sealed containers when heated
Memory trick: 'Pressure follows heat when volume can't retreat' — Gay-Lussac's rule.