PADI Open Water Diver | Comprehensive Study Guide,
Practice Exam, Questions & Answers, PADI
Certification Exam Prep, Scuba Diving Fundamentals,
Dive Planning, Underwater Navigation, Buoyancy
Control, Dive Safety, Diving Equipment, Emergency
Procedures, Marine Life Awareness, Detailed
Rationales, Complete Review
Question 1: If an object is neutrally buoyant in fresh water, what will happen
when it is placed into salt water?
A. It will sink.
B. It will remain neutrally buoyant.
C. It will either sink or float depending on its shape.
D. It will float.
CORRECT ANSWER: D. It will float.
Rationale:Salt water is denser than fresh water because of dissolved salts and minerals .
This increased density provides greater upward buoyant force. An object that is neutrally
buoyant in fresh water will therefore be positively buoyant in salt water and will float .
Question 2: What happens to an air-filled, flexible container like a balloon
when it is taken to the bottom of a swimming pool?
A. The balloon gets bigger and the air inside becomes less dense.
B. The balloon gets smaller and the air inside becomes more dense.
C. The balloon gets bigger and the air inside becomes more dense.
D. The balloon gets smaller and the air inside becomes less dense.
CORRECT ANSWER: B. The balloon gets smaller and the air inside becomes
more dense.
Rationale:As depth increases, water pressure increases. This pressure compresses the
air inside the flexible balloon, causing its volume to decrease . Because the same
amount of air now occupies a smaller volume, its density increases, and the air
molecules are pushed closer together .
Question 3: If you trap air in an inverted glass at the surface and take it down
to 10 meters, what will happen to the air space?
A. It will become half the size.
B. It will not change in size.
C. It will become one-third the size.
D. It will become two-thirds the size.
CORRECT ANSWER: A. It will become half the size.
Rationale:At 10 meters of seawater, the absolute pressure is 2 bar (1 bar from the
atmosphere + 1 bar from the water). According to Boyle's Law, the volume of a gas is
,inversely proportional to its pressure . Therefore, at double the pressure, the volume is
reduced to half of its original size .
Question 4: A diver is unable to equalize their ears and sinuses during descent.
This is most likely due to:
A. Seasickness.
B. Anxiety.
C. A cold, allergy, or other medical problem causing congestion.
D. Heart disease and high blood pressure.
CORRECT ANSWER: C. A cold, allergy, or other medical problem causing
congestion.
Rationale:Congestion from a cold or allergy can block the Eustachian tubes and sinus
passages, preventing the flow of air required to equalize pressure in these air spaces .
Attempting to dive with such a condition can make equalization difficult or impossible,
potentially leading to injury .
Question 5: During a descent, your ears or sinuses begin to hurt. What is the
most likely cause and what should you do?
A. Your air spaces are fully equalized; continue the descent.
B. Your mask strap is too tight; loosen it.
C. You are feeling a squeeze and need to equalize; stop your descent and ascend slightly
to try again.
D. Your mask is too small; surface to change it.
CORRECT ANSWER: C. You are feeling a squeeze and need to equalize; stop
your descent and ascend slightly to try again.
Rationale:Pain in the ears or sinuses during descent is a classic symptom of a
"squeeze," indicating a pressure imbalance where the pressure outside is greater than
the pressure inside the air space . The recommended action is to stop the descent,
ascend a meter or two to reduce the pressure differential, and attempt to equalize
gently .
Question 6: Where is the recommended location to secure your alternate air
source?
A. Loose by your side so you can find it fast.
B. In the triangle area formed by your chin and the lower corners of your rib cage.
C. To the base of your cylinder.
D. On the back of your BCD between your shoulder blades.
CORRECT ANSWER: B. In the triangle area formed by your chin and the lower
corners of your rib cage.
Rationale:The alternate air source should be secured within the "triangle area" defined
by the chin and the lower corners of the rib cage . This is the standard and safest
,location as it keeps the regulator readily accessible to both the primary diver and their
buddy in an emergency .
Question 7: Which of the following is the primary cause of lung overexpansion
injuries in scuba diving?
A. Diving without a buddy.
B. Continuing a dive when not properly weighted.
C. Not drinking enough water before a dive.
D. Holding your breath while ascending.
CORRECT ANSWER: D. Holding your breath while ascending.
Rationale:The most important rule in scuba diving is to breathe continuously and never
hold your breath . As a diver ascends, the pressure decreases, and the air in the lungs
expands. If a diver holds their breath and ascends, the expanding air can over-expand
and rupture the lungs, causing a serious and potentially fatal injury .
Question 8: If a scuba cylinder allows a diver to breathe for 60 minutes at the
surface, how long would it last at 20 meters of depth, assuming the same
breathing rate?
A. 60 minutes
B. 20 minutes
C. 30 minutes
D. 15 minutes
CORRECT ANSWER: B. 20 minutes
Rationale:At 20 meters, the absolute pressure is 3 bar (1 atmosphere at the surface + 2
atmospheres from the 20 meters of water) . The diver's body requires air at this ambient
pressure, meaning they will consume air from the cylinder at a rate proportional to the
pressure. The air will last one-third as long as it would at the surface: 60 minutes / 3 =
20 minutes .
Question 9: How often is a visual inspection of a scuba cylinder by a dive
center required?
A. Once a year.
B. Once every two years.
C. Every six months.
D. Every five years.
CORRECT ANSWER: A. Once a year.
Rationale:A scuba cylinder requires a visual inspection by a qualified professional at
least once a year. This inspection is to check for internal corrosion, contamination, or
other damage that could compromise the cylinder's safety . A hydrostatic pressure test,
which is different, is required every five years .
, Question 10: What is the primary difference between a DIN valve and a Yoke
valve on a scuba cylinder?
A. DIN valves are made of durable plastic.
B. DIN valves have a spring-operated shutoff valve.
C. DIN valves have an o-ring in them.
D. DIN valves have threaded openings to screw the regulator into.
CORRECT ANSWER: D. DIN valves have threaded openings to screw the
regulator into.
Rationale:The DIN (Deutsche Industrie Norm) valve system features a threaded
opening into which the regulator first stage is screwed directly . The yoke system is a
clamp-style fitting that secures the regulator over an o-ring on the cylinder valve .
Question 11: Which of the following is an important part of proper scuba
cylinder care?
A. Sand and repaint it every year.
B. Dry it in the sun.
C. Keep some air in it.
D. Have it pressure tested every month.
CORRECT ANSWER: C. Keep some air in it.
Rationale:Scuba cylinders should always be stored with some air pressure (e.g., 200 psi)
to prevent moist air and contaminants from entering the tank, which can cause internal
corrosion . Drying in the sun is not recommended as it can damage valves, and
sanding/painting is not a standard maintenance practice .
Question 12: When looking at an object underwater, it often appears:
A. Larger and/or nearer than it actually is.
B. Larger and/or further away than it actually is.
C. Smaller and/or further away than it actually is.
D. The same size and distance as it is on the surface.
CORRECT ANSWER: A. Larger and/or nearer than it actually is.
Rationale:This is due to the refraction of light. As light passes from the water into the
air space of your mask, the light rays bend . This refraction causes objects underwater to
appear approximately 25% closer and 25% larger than they really are .
Question 13: What is the primary reason you cannot easily tell where a sound
is coming from underwater?
A. Sound travels faster in water than in air.
B. Light travels slower in water than in air.
C. Aquatic life creates too much background noise.
D. The water's density distorts sound waves.
Practice Exam, Questions & Answers, PADI
Certification Exam Prep, Scuba Diving Fundamentals,
Dive Planning, Underwater Navigation, Buoyancy
Control, Dive Safety, Diving Equipment, Emergency
Procedures, Marine Life Awareness, Detailed
Rationales, Complete Review
Question 1: If an object is neutrally buoyant in fresh water, what will happen
when it is placed into salt water?
A. It will sink.
B. It will remain neutrally buoyant.
C. It will either sink or float depending on its shape.
D. It will float.
CORRECT ANSWER: D. It will float.
Rationale:Salt water is denser than fresh water because of dissolved salts and minerals .
This increased density provides greater upward buoyant force. An object that is neutrally
buoyant in fresh water will therefore be positively buoyant in salt water and will float .
Question 2: What happens to an air-filled, flexible container like a balloon
when it is taken to the bottom of a swimming pool?
A. The balloon gets bigger and the air inside becomes less dense.
B. The balloon gets smaller and the air inside becomes more dense.
C. The balloon gets bigger and the air inside becomes more dense.
D. The balloon gets smaller and the air inside becomes less dense.
CORRECT ANSWER: B. The balloon gets smaller and the air inside becomes
more dense.
Rationale:As depth increases, water pressure increases. This pressure compresses the
air inside the flexible balloon, causing its volume to decrease . Because the same
amount of air now occupies a smaller volume, its density increases, and the air
molecules are pushed closer together .
Question 3: If you trap air in an inverted glass at the surface and take it down
to 10 meters, what will happen to the air space?
A. It will become half the size.
B. It will not change in size.
C. It will become one-third the size.
D. It will become two-thirds the size.
CORRECT ANSWER: A. It will become half the size.
Rationale:At 10 meters of seawater, the absolute pressure is 2 bar (1 bar from the
atmosphere + 1 bar from the water). According to Boyle's Law, the volume of a gas is
,inversely proportional to its pressure . Therefore, at double the pressure, the volume is
reduced to half of its original size .
Question 4: A diver is unable to equalize their ears and sinuses during descent.
This is most likely due to:
A. Seasickness.
B. Anxiety.
C. A cold, allergy, or other medical problem causing congestion.
D. Heart disease and high blood pressure.
CORRECT ANSWER: C. A cold, allergy, or other medical problem causing
congestion.
Rationale:Congestion from a cold or allergy can block the Eustachian tubes and sinus
passages, preventing the flow of air required to equalize pressure in these air spaces .
Attempting to dive with such a condition can make equalization difficult or impossible,
potentially leading to injury .
Question 5: During a descent, your ears or sinuses begin to hurt. What is the
most likely cause and what should you do?
A. Your air spaces are fully equalized; continue the descent.
B. Your mask strap is too tight; loosen it.
C. You are feeling a squeeze and need to equalize; stop your descent and ascend slightly
to try again.
D. Your mask is too small; surface to change it.
CORRECT ANSWER: C. You are feeling a squeeze and need to equalize; stop
your descent and ascend slightly to try again.
Rationale:Pain in the ears or sinuses during descent is a classic symptom of a
"squeeze," indicating a pressure imbalance where the pressure outside is greater than
the pressure inside the air space . The recommended action is to stop the descent,
ascend a meter or two to reduce the pressure differential, and attempt to equalize
gently .
Question 6: Where is the recommended location to secure your alternate air
source?
A. Loose by your side so you can find it fast.
B. In the triangle area formed by your chin and the lower corners of your rib cage.
C. To the base of your cylinder.
D. On the back of your BCD between your shoulder blades.
CORRECT ANSWER: B. In the triangle area formed by your chin and the lower
corners of your rib cage.
Rationale:The alternate air source should be secured within the "triangle area" defined
by the chin and the lower corners of the rib cage . This is the standard and safest
,location as it keeps the regulator readily accessible to both the primary diver and their
buddy in an emergency .
Question 7: Which of the following is the primary cause of lung overexpansion
injuries in scuba diving?
A. Diving without a buddy.
B. Continuing a dive when not properly weighted.
C. Not drinking enough water before a dive.
D. Holding your breath while ascending.
CORRECT ANSWER: D. Holding your breath while ascending.
Rationale:The most important rule in scuba diving is to breathe continuously and never
hold your breath . As a diver ascends, the pressure decreases, and the air in the lungs
expands. If a diver holds their breath and ascends, the expanding air can over-expand
and rupture the lungs, causing a serious and potentially fatal injury .
Question 8: If a scuba cylinder allows a diver to breathe for 60 minutes at the
surface, how long would it last at 20 meters of depth, assuming the same
breathing rate?
A. 60 minutes
B. 20 minutes
C. 30 minutes
D. 15 minutes
CORRECT ANSWER: B. 20 minutes
Rationale:At 20 meters, the absolute pressure is 3 bar (1 atmosphere at the surface + 2
atmospheres from the 20 meters of water) . The diver's body requires air at this ambient
pressure, meaning they will consume air from the cylinder at a rate proportional to the
pressure. The air will last one-third as long as it would at the surface: 60 minutes / 3 =
20 minutes .
Question 9: How often is a visual inspection of a scuba cylinder by a dive
center required?
A. Once a year.
B. Once every two years.
C. Every six months.
D. Every five years.
CORRECT ANSWER: A. Once a year.
Rationale:A scuba cylinder requires a visual inspection by a qualified professional at
least once a year. This inspection is to check for internal corrosion, contamination, or
other damage that could compromise the cylinder's safety . A hydrostatic pressure test,
which is different, is required every five years .
, Question 10: What is the primary difference between a DIN valve and a Yoke
valve on a scuba cylinder?
A. DIN valves are made of durable plastic.
B. DIN valves have a spring-operated shutoff valve.
C. DIN valves have an o-ring in them.
D. DIN valves have threaded openings to screw the regulator into.
CORRECT ANSWER: D. DIN valves have threaded openings to screw the
regulator into.
Rationale:The DIN (Deutsche Industrie Norm) valve system features a threaded
opening into which the regulator first stage is screwed directly . The yoke system is a
clamp-style fitting that secures the regulator over an o-ring on the cylinder valve .
Question 11: Which of the following is an important part of proper scuba
cylinder care?
A. Sand and repaint it every year.
B. Dry it in the sun.
C. Keep some air in it.
D. Have it pressure tested every month.
CORRECT ANSWER: C. Keep some air in it.
Rationale:Scuba cylinders should always be stored with some air pressure (e.g., 200 psi)
to prevent moist air and contaminants from entering the tank, which can cause internal
corrosion . Drying in the sun is not recommended as it can damage valves, and
sanding/painting is not a standard maintenance practice .
Question 12: When looking at an object underwater, it often appears:
A. Larger and/or nearer than it actually is.
B. Larger and/or further away than it actually is.
C. Smaller and/or further away than it actually is.
D. The same size and distance as it is on the surface.
CORRECT ANSWER: A. Larger and/or nearer than it actually is.
Rationale:This is due to the refraction of light. As light passes from the water into the
air space of your mask, the light rays bend . This refraction causes objects underwater to
appear approximately 25% closer and 25% larger than they really are .
Question 13: What is the primary reason you cannot easily tell where a sound
is coming from underwater?
A. Sound travels faster in water than in air.
B. Light travels slower in water than in air.
C. Aquatic life creates too much background noise.
D. The water's density distorts sound waves.
