NAUI Diving Physics & Physiology Practice Questions — 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.

Question 8: What is the partial pressure of nitrogen in air (78% N2) at a depth of 99 feet (4 ATA)?

0.78 ATA
1.56 ATA
3.12 ATA (Correct answer)
4.00 ATA

Correct answer: 3.12 ATA

Dalton's Law: partial pressure = fraction × total pressure, so 0.78 × 4 ATA = 3.12 ATA of nitrogen.

Question 9: Decompression sickness (DCS) Type II involves which body systems, making it more serious than Type I?

Skin and lymphatic system only
Joints and muscles only
Neurological and cardiopulmonary systems (Correct answer)
Ears and sinuses only

Correct answer: Neurological and cardiopulmonary systems

Type II DCS affects the spinal cord, brain, and lungs (chokes), and is considered a medical emergency requiring immediate recompression.

Question 10: A diver ascends too quickly after a deep dive. Nitrogen bubbles form in the tissues. What physical law best describes why bubbles form during ascent?

Gay-Lussac's Law — pressure and temperature relationship
Henry's Law — gas dissolving from solution as pressure drops (Correct answer)
Archimedes' Principle — buoyancy forces on the diver
Dalton's Law — partial pressures of mixed gases

Correct answer: Henry's Law — gas dissolving from solution as pressure drops

Henry's Law states that gas dissolved in liquid will come out of solution when pressure decreases, which is why rapid ascent causes nitrogen bubble formation.

Question 11: Sound travels approximately how much faster in water than in air?

About the same speed
Approximately 2 times faster
Approximately 4 times faster (Correct answer)
About 10 times faster

Correct answer: Approximately 4 times faster

Sound travels at about 1,500 m/s in water versus approximately 340 m/s in air, making it roughly 4 times faster underwater.

Question 12: What physiological effect does cold water have on a diver's susceptibility to nitrogen narcosis?

Cold water reduces narcosis effects
Cold water increases narcosis susceptibility (Correct answer)
Temperature has no effect on narcosis
Cold water causes narcosis only above 40 feet

Correct answer: Cold water increases narcosis susceptibility

Cold water, along with anxiety and exertion, increases a diver's susceptibility to nitrogen narcosis, lowering the effective depth threshold.

Question 13: The 'afterdrop' phenomenon after a cold dive refers to what?

Drop in tank pressure after surfacing
Continued core temperature fall after exiting cold water (Correct answer)
Sudden buoyancy loss at the surface
Pressure drop in the ears after equalization

Correct answer: Continued core temperature fall after exiting cold water

Afterdrop occurs when cold blood from the extremities returns to the core after exiting the water, causing core temperature to continue falling even after warming begins.

Question 14: At what depth does the maximum recommended partial pressure of oxygen (1.4 ATA for working dives) occur when breathing normal air (21% O2)?

Approximately 187 feet (57 m) (Correct answer)
Approximately 218 feet (66 m)
Approximately 130 feet (40 m)
Approximately 100 feet (30 m)

Correct answer: Approximately 187 feet (57 m)

PO2 = 0.21 × total pressure; solving for 1.4 ATA: total pressure = 1.4/0.21 ≈ 6.67 ATA, which equals about 187 feet of seawater.

Question 15: A diver experiences pain in the ear during descent that stops only when they ascend slightly. What is the most likely cause?

Outer ear squeeze from a tight hood
Middle ear barotrauma due to failed equalization (Correct answer)
Inner ear decompression sickness
Nitrogen narcosis affecting hearing

Correct answer: Middle ear barotrauma due to failed equalization

Failure to equalize the middle ear during descent causes increasing pressure differential across the eardrum, resulting in pain and potential rupture.

Question 16: Which of the following best describes the term 'residual nitrogen' in dive planning?

Nitrogen remaining in the tank after a dive
Excess nitrogen dissolved in tissues from a previous dive (Correct answer)
Nitrogen that could not be breathed due to depth
Nitrogen released from tissues during decompression stops

Correct answer: Excess nitrogen dissolved in tissues from a previous dive

Residual nitrogen is the excess dissolved nitrogen that remains in body tissues after a dive that has not yet been eliminated through normal breathing.

Question 17: Hyperventilation before a breath-hold dive is dangerous because it does what?

Increases blood oxygen to dangerous levels
Removes CO2, delaying the urge to breathe until hypoxia causes blackout (Correct answer)
Causes nitrogen to dissolve rapidly into tissue
Raises blood pressure, risking arterial gas embolism

Correct answer: Removes CO2, delaying the urge to breathe until hypoxia causes blackout

Hyperventilation lowers CO2 levels, which suppresses the breathing reflex, allowing a breath-hold diver to become hypoxic and lose consciousness before feeling the urge to breathe.

Question 18: When using the NAUI dive tables, what does 'surface interval time' (SIT) determine for a repetitive dive?

The maximum depth allowed on the next dive
How much residual nitrogen has been eliminated before the next dive (Correct answer)
The required decompression stop depth
The total allowable bottom time for the entire dive day

Correct answer: How much residual nitrogen has been eliminated before the next dive

The surface interval allows residual nitrogen to off-gas; the longer the SIT, the lower the repetitive group letter and the more bottom time available on the next dive.

Question 19: What is the effect of increased water density on a diver's buoyancy compared to fresh water?

Saltwater makes divers less buoyant due to higher resistance
Saltwater makes divers more buoyant because denser water exerts greater upward force (Correct answer)
Fresh water and saltwater buoyancy are identical
Buoyancy is determined only by the diver's weight, not water type

Correct answer: Saltwater makes divers more buoyant because denser water exerts greater upward force

Saltwater (density ~1.025 g/cm³) exerts more upward buoyant force than fresh water (1.0 g/cm³), so divers typically need extra weight when diving in saltwater.

Question 20: Which condition describes a diver who ascends rapidly from a deep dive and develops chest pain, coughing, and shortness of breath?

Nitrogen narcosis
Pulmonary over-inflation syndrome (air embolism) (Correct answer)
Middle ear squeeze
Carbon monoxide poisoning

Correct answer: Pulmonary over-inflation syndrome (air embolism)

Rapid ascent with breath-holding or airway obstruction can cause lung over-expansion, leading to arterial gas embolism (AGE) with the symptoms described.

Question 21: How does increased depth affect the rate at which a diver's scuba tank is depleted?

Tank depletion rate stays constant regardless of depth
Tank depletes slower at depth because pressure compresses the air
Tank depletes faster because the diver breathes denser, higher-pressure air (Correct answer)
Tank depletion depends only on the diver's breathing rate, not depth

Correct answer: Tank depletes faster because the diver breathes denser, higher-pressure air

At greater depth, air density increases proportionally with pressure, so each breath consumes more air molecules, depleting the tank proportionally faster.

NAUI Diving Physics & Physiology Practice Questions

A diver descends from the surface to 66 feet (20 m).
What is the absolute pressure at that depth in ATA?

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