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52 Cards in this Set

  • Front
  • Back
What is refraction?
The bending of light as light goes from one medium to another, due to change in speed of light in different media.
The bending of light as light goes from one medium to another is called ____________
Refraction.
Why does an object look "bent" when placed in water?
Refraction, the bending of light as light goes from one medium to another, due to change in speed of light in different media.
Do objects in water appear closer than they really are, or farther away than they really are? By how much?
Closer, due to refraction. Objects appear 25% closer.
How much closer do objects appear underwater?
25%
What is the magnification of objects underwater?
4/3, or 33%. So if you think you see a 4m long shark, it's really 3m long.
Do objects look 25% closer underwater or 33% closer underwater?
25% closer, 33% larger.
What is visual reversal?
When objects are in cloudy water, they are obscured, which the eye associates with being further away than they really are.
Do objects in cloudy water look further away or closer than they really are? Why?
Further away due to visual reversal.
What is gauge pressure?
The pressure of the water without the atmosphere. 33' = 1 atmosphere gauge.
What is absolute pressure?
Gauge pressure + 1 atmosphere. (If at sea level. Less at altitude). 33' = 2 atmospheres absolute = 2 ATA.
What is the abbreviation ATA?
ATmospheres Absolute.
What is ambient pressure?
Surrounding pressure = absolute pressure.
Two of these are the same. Which ones? Ambient Pressure; Gauge Pressure; Absolute Pressure.
Ambient = Absolute.

Gauge = Absolute - 1 atmosphere.
What is Dalton's Law?
In a mixture of gases, each gas exerts its individual pressure independent of other gases in the mixture (partial pressure).
Which law asserts that pressures of mixed gasses are independent?
Dalton's Law.
What is surface equivalency?
The fraction of a gas you would have to breathe at the surface to produce the same effect at a particular gas, e.g., if air has 0.5% CO, breathing it at 132 feet would be the equivalent of breathing a 2.5% CO mix.
What is Henry's Law?
If pressure decreases on a liquid, dissolved gases come out of solution.
Which law dictates that if pressure decreases on a liquid, gas comes out of solution?
Henry's Law.
What is Boyle's Law?
Pressure is inversely related to volume.
Which law says that at 33' the pressure is 2 ATA?
Boyle's Law.
What is gas tension?
The pressure exerted by gasses dissolved in a liquid. The more gas that is dissolved in a liquid, the greater the gas tension.
What is supersaturation?
When gas is dissolved in a liquid at equilibrium, then surface pressure is reduced, gas tension becomes higher than the surface tension, and the gas comes out of solution.
What is conduction?
Transmission of heat by direct contact.
What is transmission of heat by direct contact called?
Conduction.
What is convection?
Transmission of heat by fluids.
What is transmission of heat by fluids called?
Convection.
What is radiation?
Transmission of heat by electromagnetic waves.
What is the transmission of heat by electromagnetic waves called?
Radiation.
What are the three ways heat is transmitted?
Radiation, convection, and conduction.
Which of the three ways heat is transmitted is most important to diving?
Conduction.
Water conducts heat how many times faster than in air?
20 times.
Which does water conduct 20 times faster, sound or heat?
Heat.
How much larger does refraction make objects look underwater?
33%, or a ratio of 4:3.
Water conducts sound how many times faster than in air?
4 times.
Which does water conduct 4 times faster, sound or heat?
Sound.
What does a cubic foot of seawater weigh?
64 pounds.
Which weighs 64 pounds, a cubic foot of seawater or fresh water?
Seawater.
What does a cubic foot of fresh water weigh?
62.4 pounds.
Which weighs 62.4 pounds, a cubic foot of seawater or fresh water?
Fresh water.
How many feet of seawater adds one atmosphere of pressure?
33.
How many feet of fresh water adds one atmosphere of pressure?
34.
Diving 33 feet adds one atmosphere of pressure in which, seawater or fresh water?
Seawater.
How do you convert Fahrenheit to Rankine?
Fahrenheit + 460
What is the temperature scale that starts from absolute zero but uses degrees the same size as Fahrenheit?
Rankine.
Buoyancy = Weight of Object - Weight of ___________.
Displaced water of the object.
How much does pressure change for every degree Fahrenheit?
5 PSI for every 1 degree F.
If a tank starts at 3000 psi at 70F, and the tank is chilled in the water to 55F, what will the pressure be?
2925 PSI - 5 PSI for every degree, and (70 - 55) = 15, 15 x 5 = 75 PSI difference. 3000 - 75 = 2925 PSI.
What is the pressure, volume, temperature formula?
(P1 x V1) / T1 = (P2 x V2) / T2.

Remember to convert F to Rankine (F + 460).
Why is water able to conduct hear more efficiently than air?
Water is more dense than air.
What is the relationship between PSI and ATA?
14.7 PSI = 1 ATA.
If a tank is filled to 3000 PSI, how many atmospheres of gas is that?
~200 ATA.

3000 PSI / (14.7 PSI / 1 ATA) = 200.