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Boyle's law pressure calculation

Aviation Mechanic General (AMG) practice question 19 of 20 on Physics for Aviation. ACS element AM.I.J.K6 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA cylinder contains 8 ft3 of nitrogen at 300 psia. If the temperature is held constant and the volume is reduced to 6 ft3, what is the new pressure?

  1. A400 psia
  2. B225 psia
  3. C2,400 psia
Show the answer and explanation

Correct answer: A. 400 psia

  • A — correct Boyle's law: V1P1 = V2P2. 8 × 300 = 6 × P2, so P2 = 2,400 ÷ 6 = 400 psia. Reducing the volume raises the absolute pressure in inverse proportion.
  • B — incorrect This comes from multiplying by 6 and dividing by 8, which would be a pressure decrease. Compressing a gas into a smaller volume increases its pressure.
  • C — incorrect 2,400 is the product V1 × P1 and must still be divided by the new volume of 6 ft3 to obtain the new pressure.

BACKGROUND

Robert Boyle discovered that when the temperature of an enclosed gas is held constant and its absolute pressure is doubled, its volume is reduced to half. Boyle's law is stated: the volume of an enclosed dry gas varies inversely with its absolute pressure, provided the temperature remains constant. The working formula is Volume 1 × Pressure 1 = Volume 2 × Pressure 2, and pressure must be in absolute units. Aviation applications include CO2 bottles for life rafts, compressed oxygen and acetylene tanks for welding, air brakes and shock absorbers, and oxygen tanks for high-altitude flight.

STUDY TIP

Write V1P1 = V2P2, make sure pressures are absolute, and check that a smaller volume produces a larger pressure before accepting your answer.

KEY POINTS

  • Boyle's law: volume varies inversely with absolute pressure at constant temperature
  • V1P1 = V2P2
  • Pressure must be expressed in absolute units (psia)

SOURCES

  • FAA-H-8083-30B ch05 "Boyle's Law"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.