NAUI Diving Physics & Physiology 2 — Questions and Answers
Question 1: A diver descends from the surface to 66 feet (20 m). What is the absolute pressure at that depth in ATA?
- 2 ATA
- 3 ATA (Correct answer)
- 4 ATA
- 1.5 ATA
Correct answer: 3 ATA
66 feet of seawater equals 2 atmospheres of water pressure plus 1 ATA at the surface, totaling 3 ATA.
Question 2: Which physiological condition results from breathing high partial pressures of oxygen at depth?
- Nitrogen narcosis
- Oxygen toxicity (Correct answer)
- Carbon dioxide retention
- Hypoxia
Correct answer: Oxygen toxicity
Breathing oxygen at partial pressures above 1.6 ATA can cause central nervous system (CNS) oxygen toxicity, leading to convulsions.
Question 3: What happens to the volume of a flexible air pocket in a diver's body (like a sinus) during ascent if it cannot equalize?
- It stays the same due to body pressure
- It decreases, causing a squeeze
- It expands, potentially causing barotrauma (Correct answer)
- It dissolves into surrounding tissue
Correct answer: It expands, potentially causing barotrauma
During ascent, decreasing pressure causes trapped gas to expand according to Boyle's Law, which can rupture surrounding tissue if it cannot vent.
Question 4: A scuba tank filled to 3000 psi at 70°F is left in a hot car where temperature rises to 140°F. What happens to the tank pressure?
- Pressure decreases because gas expands
- Pressure increases due to Gay-Lussac's Law (Correct answer)
- Pressure stays the same because the tank is rigid
- Pressure drops to zero as gas escapes
Correct answer: Pressure increases due to Gay-Lussac's Law
Gay-Lussac's Law states that at constant volume, pressure increases proportionally with absolute temperature, so the tank pressure will rise.
Question 5: What is the primary cause of nitrogen narcosis during scuba diving?
- Elevated CO2 levels in the bloodstream
- Narcotic effect of nitrogen at high partial pressures (Correct answer)
- Oxygen deprivation at depth
- Helium replacing nitrogen in the breathing mix
Correct answer: Narcotic effect of nitrogen at high partial pressures
Nitrogen at high partial pressures (typically below 100 feet) exerts an anesthetic effect on the nervous system similar to alcohol intoxication.
Question 6: Light refraction through a flat dive mask causes underwater objects to appear how?
- Smaller and farther away than actual
- Larger and closer than actual (Correct answer)
- The same size but blurry
- Inverted and distorted
Correct answer: Larger and closer than actual
The air-water interface in a flat mask refracts light, making objects appear about 25% larger and 33% closer than they actually are.
Question 7: Which law explains why a diver must breathe more air per breath at 99 feet (30 m) than at the surface?
- Henry's Law
- Dalton's Law
- Boyle's Law (Correct answer)
- Charles's Law
Correct answer: Boyle's Law
Boyle's Law explains that at 4 ATA (99 feet), gas is compressed to one-quarter its surface volume, so four times as many molecules are needed to fill the lungs.
NAUI Diving Physics & Physiology 2
A diver descends from the surface to 66 feet (20 m).
What is the absolute pressure at that depth in ATA?