PADI Physics and Gas Laws 4 — Questions and Answers
Question 1: A diver's air tank pressure drops from 3000 psi to 750 psi during a dive. The ratio of remaining air to starting air is:
- 1:4 (Correct answer)
- 1:2
- 3:4
- 1:3
Correct answer: 1:4
750 psi remaining out of 3000 psi total = 750/3000 = 1:4 ratio.
Question 2: Gay-Lussac's Law describes the relationship between pressure and temperature at constant:
- Volume (Correct answer)
- Mass
- Partial pressure
- Density
Correct answer: Volume
Gay-Lussac's Law applies at constant volume, showing pressure is proportional to absolute temperature.
Question 3: At depth, nitrogen narcosis is thought to be caused by:
- The increased partial pressure of nitrogen affecting nerve membranes (Correct answer)
- Nitrogen bubbles forming in the bloodstream
- Nitrogen reacting chemically with hemoglobin
- Reduced oxygen levels in the brain
Correct answer: The increased partial pressure of nitrogen affecting nerve membranes
High partial pressures of nitrogen (and other inert gases) dissolve into nerve cell membranes, impairing neural function.
Question 4: What is the gauge pressure at 66 feet (20 m) of seawater?
- 2 atm (29.4 psi) (Correct answer)
- 3 atm (44.1 psi)
- 1 atm (14.7 psi)
- 4 atm (58.8 psi)
Correct answer: 2 atm (29.4 psi)
Gauge pressure excludes atmospheric pressure: 66 ft / 33 ft per atm = 2 atm gauge.
Question 5: Water absorbs heat from a diver's body much faster than air because water has a higher:
- Thermal conductivity (Correct answer)
- Buoyancy
- Viscosity
- Salinity
Correct answer: Thermal conductivity
Water conducts heat about 25 times more efficiently than air, making hypothermia a significant risk for divers.
Question 6: Which gas law directly explains why a scuba regulator must reduce tank pressure in two stages to deliver breathable air?
- Boyle's Law (Correct answer)
- Dalton's Law
- Henry's Law
- Gay-Lussac's Law
Correct answer: Boyle's Law
Boyle's Law governs the relationship between pressure and volume — the regulator stages reduce pressure while managing the corresponding volume changes.
Question 7: Archimedes' Principle states that a submerged object experiences an upward buoyant force equal to:
- The weight of the fluid it displaces (Correct answer)
- The weight of the object itself
- The pressure at its depth times its surface area
- Half the weight of the surrounding water
Correct answer: The weight of the fluid it displaces
Archimedes' Principle: buoyant force equals the weight of displaced fluid, which is why objects float when they displace their own weight in water.
PADI Physics and Gas Laws 4
A diver's air tank pressure drops from 3000 psi to 750 psi during a dive.
The ratio of remaining air to starting air is: