PADI - Professional Association of Diving Instructors Diving Physics and Gas Laws Questions and Answers — Questions and Answers
Question 1: According to Boyle's Law, if a flexible container with 6 liters of air at the surface (1 ATA) is taken to a depth of 20 meters (3 ATA), what will its new volume be?
- 4 liters
- 3 liters
- 2 liters (Correct answer)
- 1.5 liters
Correct answer: 2 liters
Boyle's Law states that the volume of a gas is inversely proportional to the pressure, assuming constant temperature (P1V1 = P2V2). At the surface, P1 = 1 ATA and V1 = 6 liters. At 20 meters, the pressure (P2) is 3 ATA. To find the new volume (V2), the formula is V2 = (P1 * V1) / P2. So, V2 = (1 ATA * 6 L) / 3 ATA = 2 liters.
Question 2: A diver is using a standard air tank (approximately 21% oxygen, 79% nitrogen) at a depth of 30 meters where the ambient pressure is 4 ATA. What is the partial pressure of nitrogen (PN2) at this depth?
- 0.84 ATA
- 3.16 ATA (Correct answer)
- 4.00 ATA
- 0.79 ATA
Correct answer: 3.16 ATA
Dalton's Law states that the total pressure of a gas mixture is the sum of the partial pressures of its component gases. To find the partial pressure of a specific gas, multiply the percentage of that gas by the total ambient pressure. At 30 meters, the ambient pressure is 4 ATA. Therefore, the partial pressure of nitrogen (PN2) is 0.79 * 4 ATA = 3.16 ATA.
Question 3: Which of the following gas laws is most directly related to the risk of decompression sickness and explains why inert gases like nitrogen are absorbed into a diver's tissues at depth?
- Boyle's Law
- Charles's Law
- Archimedes' Principle
- Henry's Law (Correct answer)
Correct answer: Henry's Law
Henry's Law states that the amount of gas that dissolves into a liquid is directly proportional to the partial pressure of that gas over the liquid. As a diver descends, the partial pressure of nitrogen increases, causing more nitrogen to dissolve into the body's tissues. If the diver ascends too quickly, this dissolved nitrogen can come out of solution and form bubbles, leading to decompression sickness.
Question 4: A diver notices that their submersible pressure gauge (SPG) reads a lower pressure after their tank, which was filled in a warm room, has been submerged in cold water for a while before the dive. This phenomenon is best explained by:
- Dalton's Law
- Boyle's Law
- Charles's Law (Correct answer)
- Henry's Law
Correct answer: Charles's Law
Charles's Law states that for a fixed mass of gas at a constant volume, the pressure is directly proportional to the absolute temperature. When the warm tank cools in the water, the temperature of the gas inside decreases, causing the pressure to drop.
Question 5: To achieve neutral buoyancy, a diver adds or removes air from their Buoyancy Compensator (BC). This action directly applies which physical principle?
- Archimedes' Principle (Correct answer)
- Boyle's Law
- Pascal's Law
- Dalton's Law
Correct answer: Archimedes' Principle
Archimedes' Principle states that an object submerged in a fluid is buoyed up by a force equal to the weight of the fluid it displaces. By adding air to the BC, the diver increases their volume, displaces more water, and thus increases the upward buoyant force. Releasing air has the opposite effect. This allows the diver to balance the downward force of their weight with the upward buoyant force to become neutrally buoyant.
Question 6: The most important rule in scuba diving is to never hold your breath. This rule is a direct consequence of which gas law, as it relates to the risk of lung overexpansion injury during ascent?
- Henry's Law
- Boyle's Law (Correct answer)
- Dalton's Law
- Charles's Law
Correct answer: Boyle's Law
Boyle's Law explains the inverse relationship between pressure and volume. As a diver ascends, the ambient pressure decreases. If the diver holds their breath, the air trapped in their lungs will expand. This expansion can cause a lung overexpansion injury (pulmonary barotrauma), which is why continuous breathing during ascent is critical.
PADI - Professional Association of Diving Instructors Diving Physics and Gas Laws Questions and Answers
According to Boyle's Law, if a flexible container with 6 liters of air at the surface (1 ATA) is taken to a depth of 20 meters (3 ATA), what will its new volume be?