PADI Physics and Gas Laws 2 — Questions and Answers
Question 1: A diver at 66 feet (20 m) breathes from a tank with 3000 psi. Using Boyle's Law, approximately how much air (in surface-equivalent volume) has been consumed if the tank now reads 1500 psi?
- Half the tank's surface-equivalent volume (Correct answer)
- One quarter of the tank's surface-equivalent volume
- Three quarters of the tank's surface-equivalent volume
- The same volume as at the surface
Correct answer: Half the tank's surface-equivalent volume
Pressure drop from 3000 to 1500 psi means half the tank's compressed air is gone, regardless of depth.
Question 2: Charles's Law states that at constant pressure, the volume of a gas is proportional to its:
- Absolute temperature (Correct answer)
- Density
- Partial pressure
- Molecular weight
Correct answer: Absolute temperature
Charles's Law relates gas volume directly to absolute temperature (Kelvin) at constant pressure.
Question 3: A scuba cylinder is filled to 3000 psi at 70°F (21°C). If the cylinder cools to 30°F (-1°C), what happens to the pressure inside?
- It decreases (Correct answer)
- It increases
- It stays the same
- It doubles
Correct answer: It decreases
By Gay-Lussac's Law, pressure decreases as temperature drops at constant volume.
Question 4: Which law explains why a diver's lungs could rupture if they hold their breath while ascending?
- Boyle's Law (Correct answer)
- Dalton's Law
- Henry's Law
- Charles's Law
Correct answer: Boyle's Law
Boyle's Law shows that as pressure decreases on ascent, gas volume expands — holding breath traps that expanding gas in the lungs.
Question 5: According to Dalton's Law, the partial pressure of oxygen in air at 3 ATA is:
- 0.63 ATA (Correct answer)
- 0.21 ATA
- 1.0 ATA
- 3.0 ATA
Correct answer: 0.63 ATA
Oxygen is 21% of air, so at 3 ATA: 0.21 × 3 = 0.63 ATA partial pressure.
Question 6: Henry's Law is most directly related to which diving concern?
- Decompression sickness (Correct answer)
- Oxygen toxicity
- Lung overexpansion
- Nitrogen narcosis symptoms worsening at depth
Correct answer: Decompression sickness
Henry's Law states that gas dissolves into liquid proportional to its partial pressure — the principle behind nitrogen absorption and DCS.
Question 7: A diver descends to 99 feet (30 m). The absolute pressure in ATA is:
- 4 ATA (Correct answer)
- 3 ATA
- 5 ATA
- 2 ATA
Correct answer: 4 ATA
Every 33 feet of seawater adds 1 ATA; 99 ft = 3 ATA of water pressure + 1 ATA atmosphere = 4 ATA.
PADI Physics and Gas Laws 2
A diver at 66 feet (20 m) breathes from a tank with 3000 psi.
Using Boyle's Law, approximately how much air (in surface-equivalent volume) has been consumed if the tank now reads 1500 psi?