IDC Guide

Dive Theory

Mock Exam C

PADI Instructor Development

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Constants used for Dive Theory Exams

1 litre of salt water weighs 1.03 kilograms
1 litre of fresh water weighs 1 kilogram

Pressure increases by 1 ATM every 10 metres of salt water
Pressure increases by 1 ATM every 10.3 metres of fresh water

Pressure changes per unit of salt water = 0.100 ATM/m
Pressure changes per unit of fresh water = 0.097 ATM/m


1) Sound travels _____ faster in water than in air?
a) 20
b) 14
c) 6
d) 4

2) What is the gauge pressure at 36m in sea water?
a) 3.6 atm
b) 4.55 atm
c) 3.55 atm
d) 4.6 atm

3) What is the gauge pressure at 30m in fresh water?
a) 4 atm
b) 3 atm
c) 2.91 atm
d) 1.5 atm

4) If a sealed, flexible air filled container with a volume
of 3.5 litres at 30m of sea water is taken to 20m,
what would the new volume be?
a) 14.0 litres
b) 4.66 litres
c) 3.66 litres
d) 2.50 litres

5) If an object weighs 250 kg and displaces 65 litres,
how much water needs to be displaced to achieve
neutral buoyancy in 18m of fresh water?
a) 181 litres
b) 185 litres
c) 250 litres
d) 315 litres

6) Red is the first colour to disappear underwater due
a) absorption
b) refraction
c) reflection
d) turbidity

7) The human body loses heat ____ times faster in water
than in air?
a) 4
b) 14
c) 20
d) 60

8) A scuba tank containing 0.5% of carbon monoxide at
the surface is taken to 30m. What percentage of
carbon monoxide is in the scuba tank at this depth?
a) 4%
b) 3%
c) 2%
d) 0.5%

9) If a diver breathes 100 bar of air in 20 minutes at 20m
of sea water, how much air would he breathe in 10
mins at 10m of sea water?
a) 33 bar
b) 20 bar
c) 50 bar
d) 100 bar

10) Refraction causes objects underwater to be magnified
a) 16%
b) 33%
c) 25%
d) 50%

11) In a mixture of gases, the portion of the absolute
pressure exerted by one of the gases in the mix is
a) partial pressure
b) gauge pressure
c) ambient pressure
d) atmospheric pressure

12) When you raise the pressure of a gas in contact with a
a) the liquid evaporates
b) the gas forms bubbles in the liquid
c) the liquid dissolves into the gas
d) the gas dissolves into the liquid


1) Cigarette smoking prior to a dive should be avoided
a) it reduces the body’s ability to transport oxygen
b) it increases the risk of nitrogen narcosis
c) it raises the carbon monoxide level in the blood
d) both a and c are correct

2) During a deep dive a diver begins to show signs of
gas narcosis. To stop this the diver should:
a) breathe more deeply
b) immediately ascend a few metres
c) end the dive
d) stop and hold on to something until it passes

3) Oxygen is recommended for DCS first aid because:
a) it accelerates nitrogen elimination and raises
blood oxygen levels
b) it dilates blood vessels in the limbs to reduce
limb pain
c) it forces bubbles back into solution
d) all of the above

4) The middle ear is ___ affected by pressure changes.
a) most
b) least
c) not
d) none of the above

5) Performing a forceful Valsalva accompanied by a
delayed middle ear equalization can cause _______.
a) a reverse squeeze
b) an eardrum rupture
c) an oval window rupture
d) a round window rupture

6) Which of the following is most likely to occur if a
diver ruptures an ear drum while diving in cold
a) the diver may experience vertigo
b) the diver may experience a squeeze
c) the diver may experience euphoria
d) the diver may lose consciousness

7) Common signs and symptoms of gas narcosis
a) a feeling of intoxication
b) cherry red lips and finger nail beds
c) numbness, tingling and / or paralysis
d) all of the above

8) ______ is the most serious lung over- expansion injury?
a) pneumothorax
b) mediastinal emphysema
c) air embolism
d) subcutaneous emphysema

9) Two conditions caused by a near complete failure of the
body’s temperature maintaining system are:
a) heat exhaustion and heat stroke
b) heat stroke and shallow water blackout
c) advanced hypothermia and heat exhaustion
d) advanced hypothermia and heat stroke

10) A squeeze is caused by:
a) failure to equalize a body air space
b) inert gas affecting the nervous system
c) vasoconstriction in the fingers and toes
d) the formation of silent bubbles

11) Factors that influence a diver’s susceptibility to
decompression sickness include:
a) dehydration
b) strenuous exercise during or after a dive
c) recent illness or injury
d) all of the above

12) Shallow water blackout refers to unconsciousness that
may occur during a ____________ dive during ascent
due to ___________ .
a) deep / supersaturation
b) breath-hold / increased carbon dioxide level
c) breath-hold / falling partial pressure of oxygen
d) night / dive light failure

Recreational Dive Planner

1) Diving above 300 metres requires the use of
special procedures including the conversion of:
a) actual depth to theoretical depth
b) altitude to barometric pressure
c) theoretical depth to barometric pressure
d) barometric pressure to actual depth

2) In a decompression model, the _______ sets the
maximum nitrogen pressure that a compartment
can have when a diver surfaces.
a) compartment
b) halftime
c) M-value
d) controlling tissue

3) The Recreational Dive Planner has ______ tissue
compartments and uses a 60 minute ________
for calculating washout.
a) 6 / M-value
b) 14 / M-value
c) 6 / halftime
d) 14 / halftime

4) An RDP 5 minute compartment that is full of
nitrogen would theoretically be free of all nitrogen in
_______ minutes at the surface.
a) 5 minutes
b) 30 minutes
c) 60 minutes
d) none of the above

5) The U.S. Navy tables use a ___________ halftime
whereas the RDP uses a ___________ halftime.
a) 30 minutes / 60 minutes
b) 60 minutes / 120 minutes
c) 120 minutes / 60 minutes
d) 120 minute / 80 minutes

6) The minimum recommended surface interval before
flying after a single shallow dive is:
a) 4 hours
b) 8 hours
c) 12 hours
d) 24 hours

Use the eRDPml to answer the following:

7) What is the no decompression limit for a dive to 27m?
a) 23 minutes
b) 37 minutes
c) 14 minutes
d) 29 minutes

8) A diver exits the water in pressure group J, what is
the pressure group after a 19 minute surface interval?
a) E
b) H
c) F
d) G

9) What is the minimum surface interval required between
a dive to 18 metres for 40 minutes followed by a dive
to 14 metres for 60 minutes.
a) 26 minutes
b) 27 minutes
c) 28 minutes
d) 30 minutes

10) What is your pressure group after a dive to 12 metres
for 24 minutes?
a) D
b) E
c) C
d) F

11) You’re planning a multilevel dive. The first level will be
at 30 metres for 9 minutes, the second level 20m.
What is the maximum time you can spend at 20m?
a) 8 minutes
b) 25 minutes
c) 30 minutes
d This level exceeds limits.

12) A diver completes a multilevel dive with the following
profile: 32 metres for 9 minutes, then 20 metres for
15 minutes, then 12 metres for 20 minutes.
What is the divers pressure group upon surfacing?
a) R
b) S
c) T
d) U

General Skills & Environment

1) The same object would be more buoyant in _______
water than in ________ water.
a) warm / cold
b) cold / warm
c) fresh / salt
d) salt / fresh

2) The Coriolis Effect is the name given to:
a) the circulation of major ocean currents
b) the gravitational influence of the moon
c) the earth’s major wind system
d) wave formation

3) Aquatic life injuries may be defined as:
a) bites
b) cuts, abrasions or punctures
c) stings
d) all of the above

4) Tides are caused by the influence of the ________
and ________.
a) wind / moon
b) earth’s gravity / wind
c) sun and earth
d) sun and moon

5) Most waves are caused by:
a) planetary motion
b) the moon
c) upwelling
d) wind

6) What should you do if you find yourself caught in a
current at the surface?
a) swim hard against the current
b) swim perpendicular to the current, establish
buoyancy, signal for assistance and wait for
c) swim just under the surface
d) swim with the current

7) To prevent gas narcosis:
a) equalise early and often
b) skip breathe
c) avoid deep dives
d) drink plenty of water before the dive

8) During CPR, you should administer _______
compressions followed by _________ ventilations.
a) 30 / 2
b) 15 / 1
c) 15 / 5
d) 30 / 5

9) Altitude diving requires special procedures because:
a) the partial pressure of nitrogen is increased
since the ambient pressure is increased
b) Nitrogen will come out of solution quicker
since the ambient pressure is reduced
c) the partial pressure of oxygen is increased
d) none of the above

10) A near drowning victim should be taken to see a
physician because:
a) they need to be given oxygen
b) they may need to go to a recompression chamber
c) they may be suffering mild hypothermia
d) they may suffer from secondary drowning

11) A Controlled Emergency Swimming Ascent is performed when:
a) a diver is out of air and their buddy is not close
by and they are in shallow water (12m or less)
b) a diver wants to save air for a second dive
c) a diver is low or out of air at 25m-30m
d) at the end of every dive

12) One primary dive light, one backup light and a chemical
light is recommended for:
a) each dive boat
b) each Night Dive Instructor
c) each buddy pair of night divers
d) each night diver


1) The markings that appear on a scuba cylinder
a) whether the tank is steel or aluminium
b) the date of manufacture
c) the working pressure
d) all of the above

2) Regulators that release exhaled air directly into the
water are known as:
a) free flow
b) fail safe
c) balanced
d) open circuit

3) A regulator that is designed to supply continuous air
in the result of a malfunction is called:
a) free flow
b) fail safe
c) balanced
d) open circuit

4) The purpose of the regulator first stage is to deliver
air to:
a) the second stage at breathing pressure
b) the second stage at intermediate pressure vc
c) the diver at ambient pressure
d) the diver at absolute pressure

5) A capillary depth gauge:
a) shows theoretical rather than actual depths
b) is used only during cave diving
c) is used for night diving
d) is used when diving at altitudes above 100m

6) A burst disk is:
a) caused by not equalising during descent
b) designed to stop a BCD from over-inflating
c) a safety device on a scuba tank
d) found on a snorkel

7) The J-valve was designed as a means to:
a) warn a diver that he has run low on air
b) give the diver an extra air supply
c) close the valve during the dive
d) none of the above

8) Downstream or pilot valves are found in:
a) the second stage of a modern scuba regulator
b) modern snorkels and some masks
c) scuba tank valves
d) the first stage of a modern scuba regulator

9) An environmentally sealed first stage regulator is
designed particularly for diving in:
a) extremely cold water
b) polluted water
c) cave diving
d) salt water

10) Mounting gauges in a console:
a) speeds up dive preparation
b) combines several gauges in one package
c) keeps arms clear to ease equipment donning
d) all of the above

11) A DIN connection on a scuba tank allows the first stage of the regulator
to be:
a) used on either side
b) screwed directly into the tank valve
c) unconnected quickly
d) used with a dual tank manifold

12) Who must always personally analyze the contents of an
enriched air cylinder?
a) the Divemaster
b) The diver who will use it
c) The person who filled the cylinder
d) all of the above

If you find this useful to your IDC Revision / Studies, you will be glad to hear that you can buy the full Exam Pack that includes 10 Standards and Dive Theory Mock PADI exams plus a bonus 75 question Pre-IDC Exam paper with answer keys.

Please click the link and BUY all 3 complete IDC revision packs that includes lots of revision documents and 11 practice mock exams, the exams include all the questions and answers you will need to revise to PASS the PADI IDC

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