PADI Open Water Diver | Comprehensive Study
Guide, Practice Exam, Questions & Answers, Exam
Prep Test Bank, Scuba Diving Fundamentals, Dive
Planning, Underwater Navigation, Buoyancy
Control, Dive Safety, Diving Equipment, Emergency
Procedures, Marine Life Awareness, Detailed
Rationales, Complete Review
Question 1: A diver's body is subjected to increased pressure as they descend.
According to Boyle's Law, if a diver takes a flexible, air-filled balloon to a
depth of 20 meters/66 feet, what will happen to the balloon's volume and the
density of the air inside it?
A. The volume will decrease to one-third, and the air density will triple.
B. The volume will decrease to one-half, and the air density will double.
C. The volume will increase to three times, and the air density will reduce to one-third.
D. The volume will remain the same, but the air density will increase.
CORRECT ANSWER: A. The volume will decrease to one-third, and the air
density will triple.
Rationale:At 20 meters/66 feet, the absolute pressure is 3 bar/ata (1 bar from the
atmosphere + 2 bar from the water). Boyle's Law states that at a constant temperature,
the volume of a gas is inversely proportional to pressure (P1V1 = P2V2). Therefore, the
volume will decrease to 1/3 of its original size, and since density is mass per unit
volume, the air molecules will be packed three times closer together, tripling the
density .
Question 2: An object that is neutrally buoyant in fresh water is taken to the
ocean. What will happen to the object's buoyancy in the salt water?
A. It will become negatively buoyant and sink.
B. It will remain neutrally buoyant.
C. It will become positively buoyant and float.
D. Its buoyancy will depend on the water temperature.
CORRECT ANSWER: C. It will become positively buoyant and float.
Rationale:Saltwater is denser than freshwater due to dissolved salts. This higher density
creates a greater upward buoyant force (Archimedes' principle). An object that is
neutrally buoyant in fresh water will displace the same volume of saltwater, which
weighs more, resulting in a net upward force, making the object positively buoyant .
Question 3: A diver is unable to equalize the pressure in their ears during
descent. What is the most probable cause of this issue?
A. The diver is experiencing nitrogen narcosis.
B. The diver has a cold, allergy, or another medical condition causing sinus or
Eustachian tube congestion.
,C. The diver is breathing too deeply and slowly.
D. The diver's exposure suit is too thick.
CORRECT ANSWER: B. The diver has a cold, allergy, or another medical
condition causing sinus or Eustachian tube congestion.
Rationale:To equalize, a diver must be able to pass air through the Eustachian tubes.
Congestion from a cold, allergy, or other medical condition can block these tubes,
preventing pressure equalization and leading to a painful squeeze. This is a primary
reason why diving with a cold is strongly discouraged .
Question 4: What is the most critical rule in scuba diving that must be
followed at all times to prevent serious injury?
A. Always stay within arm's reach of your buddy.
B. Always maintain neutral buoyancy.
C. Breathe continuously and never, ever hold your breath.
D. Always perform a safety stop at 5 meters.
CORRECT ANSWER: C. Breathe continuously and never, ever hold your breath.
Rationale:Holding your breath during an ascent can cause a life-threatening lung
overexpansion injury. As a diver ascends, the pressure decreases, and the air in the
lungs expands. If the airway is blocked, this expanding air can rupture the lung tissue,
forcing air into the bloodstream or chest cavity, which can lead to paralysis or death.
Breathing continuously keeps the airway open and allows expanding air to safely
escape .
Question 5: A diver's cylinder lasts 60 minutes at the surface. Assuming the
same breathing rate, how long will the same cylinder last at a depth of 20
meters/66 feet?
A. 60 minutes
B. 30 minutes
C. 20 minutes
D. 15 minutes
CORRECT ANSWER: C. 20 minutes
Rationale:At 20 meters/66 feet, the absolute pressure is 3 atmospheres (1 atm surface
+ 2 atm for the water). The air consumption rate is directly proportional to the ambient
pressure. A diver consumes air three times faster at 3 atmospheres than at 1
atmosphere. Therefore, a 60-minute cylinder at the surface will last = 20 minutes
at 20 meters .
Question 6: What is the recommended procedure if a diver experiences
difficulty breathing due to overexertion underwater?
A. Inflate the BCD to ascend rapidly.
B. Stop all activity and rest, holding onto something for support if possible.
,C. Signal "out of air" to your buddy and share air.
D. Swim quickly to the surface to get more air.
CORRECT ANSWER: B. Stop all activity and rest, holding onto something for
support if possible.
Rationale:Overexertion can lead to a feeling of breathlessness and panic, which may
cause a diver to make poor decisions. The first and most important step is to stop all
physical activity and rest. Holding onto a stationary object like a rock or the anchor line
helps the diver relax and regain normal, slow, deep breathing before continuing the
dive .
Question 7: Where is the optimal location to secure an alternate air source on
a BCD?
A. Dangling loosely from a D-ring to ensure quick access.
B. In the "triangle" area formed by the chin and the lower corners of the rib cage.
C. Secured to the cylinder valve at the base of the tank.
D. Clipped to the back of the BCD between the shoulder blades.
CORRECT ANSWER: B. In the "triangle" area formed by the chin and the lower
corners of the rib cage.
Rationale:The alternate air source should be secured in the "triangle area" in the center
of the chest. This position keeps it streamlined, protected, and easily accessible to both
the diver and a buddy in an emergency. It is typically secured with a breakaway or
quick-release clip, allowing it to be deployed smoothly .
Question 8: As a diver descends, what physical changes occur to a standard
wetsuit, and how does this affect the diver's buoyancy?
A. The neoprene compresses, becoming thinner, which decreases buoyancy.
B. The neoprene expands, becoming thicker, which increases buoyancy.
C. The neoprene remains unchanged in thickness, but buoyancy decreases.
D. The neoprene compresses, becoming thinner, which increases buoyancy.
CORRECT ANSWER: A. The neoprene compresses, becoming thinner, which
decreases buoyancy.
Rationale:The tiny bubbles of gas trapped in neoprene compress under pressure as
depth increases. This reduces the suit's volume, making it thinner and decreasing its
overall displacement. As a result, the suit provides less buoyant lift, and the diver
becomes negatively buoyant. This is why a diver must add air to their BCD during
descent to maintain neutral buoyancy .
Question 9: A diver turns a glass upside down, trapping air in it, and takes it
down to 10 meters/33 feet. What will happen to the volume of the air space
inside the glass?
, A. It will become half its original size.
B. It will remain the same size.
C. It will become one-third its original size.
D. It will become two-thirds its original size.
CORRECT ANSWER: A. It will become half its original size.
Rationale:At 10 meters/33 feet, the absolute pressure is 2 bar (1 atmosphere at the
surface + 1 atmosphere from the water). According to Boyle's Law (P1V1 = P2V2),
doubling the pressure will halve the volume of a trapped gas. Therefore, the air space
will decrease to half of what it was at the surface .
Question 10: What is the primary purpose of performing a buoyancy check at
the surface before a dive?
A. To ensure the cylinder is full of air.
B. To confirm the diver is properly weighted for the dive.
C. To check if the BCD inflator is working correctly.
D. To test the regulator for free flow.
CORRECT ANSWER: B. To confirm the diver is properly weighted for the dive.
Rationale:A buoyancy check is the standard procedure for determining if a diver has
the correct amount of weight. With an empty BCD, a normal breath of air held, and a full
cylinder, the diver should float at eye level. When they exhale, they should slowly
descend. This ensures the diver can achieve neutral buoyancy and make a safe,
controlled ascent at the end of the dive .
Question 11: Underwater, objects often appear closer and larger than they are
on the surface. What is the primary reason for this visual distortion?
A. The water absorbs red light, making objects look larger.
B. Light rays bend (refract) as they pass from water through the lens of the mask into the
air.
C. The pressure of the water compresses the eye, altering its focal length.
D. The mask glass acts as a concave lens, magnifying objects.
CORRECT ANSWER: B. Light rays bend (refract) as they pass from water
through the lens of the mask into the air.
Rationale:The speed of light is different in water than in air. When light rays from an
object travel from the water into the air space of the mask, they bend or refract. This
refraction causes the brain to perceive objects as being approximately 25% larger and
closer than they actually are .
Question 12: Why is it difficult for a diver to locate the source of a sound
underwater?
A. Water absorbs sound waves, making them very quiet.
B. Sound travels at the same speed in water as in air.
Guide, Practice Exam, Questions & Answers, Exam
Prep Test Bank, Scuba Diving Fundamentals, Dive
Planning, Underwater Navigation, Buoyancy
Control, Dive Safety, Diving Equipment, Emergency
Procedures, Marine Life Awareness, Detailed
Rationales, Complete Review
Question 1: A diver's body is subjected to increased pressure as they descend.
According to Boyle's Law, if a diver takes a flexible, air-filled balloon to a
depth of 20 meters/66 feet, what will happen to the balloon's volume and the
density of the air inside it?
A. The volume will decrease to one-third, and the air density will triple.
B. The volume will decrease to one-half, and the air density will double.
C. The volume will increase to three times, and the air density will reduce to one-third.
D. The volume will remain the same, but the air density will increase.
CORRECT ANSWER: A. The volume will decrease to one-third, and the air
density will triple.
Rationale:At 20 meters/66 feet, the absolute pressure is 3 bar/ata (1 bar from the
atmosphere + 2 bar from the water). Boyle's Law states that at a constant temperature,
the volume of a gas is inversely proportional to pressure (P1V1 = P2V2). Therefore, the
volume will decrease to 1/3 of its original size, and since density is mass per unit
volume, the air molecules will be packed three times closer together, tripling the
density .
Question 2: An object that is neutrally buoyant in fresh water is taken to the
ocean. What will happen to the object's buoyancy in the salt water?
A. It will become negatively buoyant and sink.
B. It will remain neutrally buoyant.
C. It will become positively buoyant and float.
D. Its buoyancy will depend on the water temperature.
CORRECT ANSWER: C. It will become positively buoyant and float.
Rationale:Saltwater is denser than freshwater due to dissolved salts. This higher density
creates a greater upward buoyant force (Archimedes' principle). An object that is
neutrally buoyant in fresh water will displace the same volume of saltwater, which
weighs more, resulting in a net upward force, making the object positively buoyant .
Question 3: A diver is unable to equalize the pressure in their ears during
descent. What is the most probable cause of this issue?
A. The diver is experiencing nitrogen narcosis.
B. The diver has a cold, allergy, or another medical condition causing sinus or
Eustachian tube congestion.
,C. The diver is breathing too deeply and slowly.
D. The diver's exposure suit is too thick.
CORRECT ANSWER: B. The diver has a cold, allergy, or another medical
condition causing sinus or Eustachian tube congestion.
Rationale:To equalize, a diver must be able to pass air through the Eustachian tubes.
Congestion from a cold, allergy, or other medical condition can block these tubes,
preventing pressure equalization and leading to a painful squeeze. This is a primary
reason why diving with a cold is strongly discouraged .
Question 4: What is the most critical rule in scuba diving that must be
followed at all times to prevent serious injury?
A. Always stay within arm's reach of your buddy.
B. Always maintain neutral buoyancy.
C. Breathe continuously and never, ever hold your breath.
D. Always perform a safety stop at 5 meters.
CORRECT ANSWER: C. Breathe continuously and never, ever hold your breath.
Rationale:Holding your breath during an ascent can cause a life-threatening lung
overexpansion injury. As a diver ascends, the pressure decreases, and the air in the
lungs expands. If the airway is blocked, this expanding air can rupture the lung tissue,
forcing air into the bloodstream or chest cavity, which can lead to paralysis or death.
Breathing continuously keeps the airway open and allows expanding air to safely
escape .
Question 5: A diver's cylinder lasts 60 minutes at the surface. Assuming the
same breathing rate, how long will the same cylinder last at a depth of 20
meters/66 feet?
A. 60 minutes
B. 30 minutes
C. 20 minutes
D. 15 minutes
CORRECT ANSWER: C. 20 minutes
Rationale:At 20 meters/66 feet, the absolute pressure is 3 atmospheres (1 atm surface
+ 2 atm for the water). The air consumption rate is directly proportional to the ambient
pressure. A diver consumes air three times faster at 3 atmospheres than at 1
atmosphere. Therefore, a 60-minute cylinder at the surface will last = 20 minutes
at 20 meters .
Question 6: What is the recommended procedure if a diver experiences
difficulty breathing due to overexertion underwater?
A. Inflate the BCD to ascend rapidly.
B. Stop all activity and rest, holding onto something for support if possible.
,C. Signal "out of air" to your buddy and share air.
D. Swim quickly to the surface to get more air.
CORRECT ANSWER: B. Stop all activity and rest, holding onto something for
support if possible.
Rationale:Overexertion can lead to a feeling of breathlessness and panic, which may
cause a diver to make poor decisions. The first and most important step is to stop all
physical activity and rest. Holding onto a stationary object like a rock or the anchor line
helps the diver relax and regain normal, slow, deep breathing before continuing the
dive .
Question 7: Where is the optimal location to secure an alternate air source on
a BCD?
A. Dangling loosely from a D-ring to ensure quick access.
B. In the "triangle" area formed by the chin and the lower corners of the rib cage.
C. Secured to the cylinder valve at the base of the tank.
D. Clipped to the back of the BCD between the shoulder blades.
CORRECT ANSWER: B. In the "triangle" area formed by the chin and the lower
corners of the rib cage.
Rationale:The alternate air source should be secured in the "triangle area" in the center
of the chest. This position keeps it streamlined, protected, and easily accessible to both
the diver and a buddy in an emergency. It is typically secured with a breakaway or
quick-release clip, allowing it to be deployed smoothly .
Question 8: As a diver descends, what physical changes occur to a standard
wetsuit, and how does this affect the diver's buoyancy?
A. The neoprene compresses, becoming thinner, which decreases buoyancy.
B. The neoprene expands, becoming thicker, which increases buoyancy.
C. The neoprene remains unchanged in thickness, but buoyancy decreases.
D. The neoprene compresses, becoming thinner, which increases buoyancy.
CORRECT ANSWER: A. The neoprene compresses, becoming thinner, which
decreases buoyancy.
Rationale:The tiny bubbles of gas trapped in neoprene compress under pressure as
depth increases. This reduces the suit's volume, making it thinner and decreasing its
overall displacement. As a result, the suit provides less buoyant lift, and the diver
becomes negatively buoyant. This is why a diver must add air to their BCD during
descent to maintain neutral buoyancy .
Question 9: A diver turns a glass upside down, trapping air in it, and takes it
down to 10 meters/33 feet. What will happen to the volume of the air space
inside the glass?
, A. It will become half its original size.
B. It will remain the same size.
C. It will become one-third its original size.
D. It will become two-thirds its original size.
CORRECT ANSWER: A. It will become half its original size.
Rationale:At 10 meters/33 feet, the absolute pressure is 2 bar (1 atmosphere at the
surface + 1 atmosphere from the water). According to Boyle's Law (P1V1 = P2V2),
doubling the pressure will halve the volume of a trapped gas. Therefore, the air space
will decrease to half of what it was at the surface .
Question 10: What is the primary purpose of performing a buoyancy check at
the surface before a dive?
A. To ensure the cylinder is full of air.
B. To confirm the diver is properly weighted for the dive.
C. To check if the BCD inflator is working correctly.
D. To test the regulator for free flow.
CORRECT ANSWER: B. To confirm the diver is properly weighted for the dive.
Rationale:A buoyancy check is the standard procedure for determining if a diver has
the correct amount of weight. With an empty BCD, a normal breath of air held, and a full
cylinder, the diver should float at eye level. When they exhale, they should slowly
descend. This ensures the diver can achieve neutral buoyancy and make a safe,
controlled ascent at the end of the dive .
Question 11: Underwater, objects often appear closer and larger than they are
on the surface. What is the primary reason for this visual distortion?
A. The water absorbs red light, making objects look larger.
B. Light rays bend (refract) as they pass from water through the lens of the mask into the
air.
C. The pressure of the water compresses the eye, altering its focal length.
D. The mask glass acts as a concave lens, magnifying objects.
CORRECT ANSWER: B. Light rays bend (refract) as they pass from water
through the lens of the mask into the air.
Rationale:The speed of light is different in water than in air. When light rays from an
object travel from the water into the air space of the mask, they bend or refract. This
refraction causes the brain to perceive objects as being approximately 25% larger and
closer than they actually are .
Question 12: Why is it difficult for a diver to locate the source of a sound
underwater?
A. Water absorbs sound waves, making them very quiet.
B. Sound travels at the same speed in water as in air.
