PADI IDC Revision – Physics

What causes things to look larger underwater?

Refraction

How much bigger do things appear to be underwater?

33%

What is the name of the phenomenon that makes things look smaller and further away?

Visual Reversal

What is the main cause of the phenomenon that causes things to look further away?

Turbidity

How many times faster does sound travel in water than in air?

4 times faster

Because sound travels faster underwater, where does it seem to come from?

Overhead

How much faster does heat travel in water than in air?

20 times

Why does heat travel much faster in water than in air?

Because water molecules form weak bonds between themselves.

What is the Gauge Pressure in 19 metres of salt water?

1.9 atm/bar

What is the Ambient ( sometimes called Absolute )  Pressure in 19 metres of salt water?

2.9 atm/bar

What is the Gauge Pressure in 18 metres of fresh water?

1.7 atm/bar (1.8 divide by 1.03)

Is the Gauge Pressure for a given depth  in salt water be the same/greater/less than the same depth of fresh water?

Greater than

If a balloon is filled to 2 litres at 45 metres, and then released, assuming that it doesn’t explode, what will it’s volume be upon reaching the surface?

11 litres
(Using box method.. 2 x 5.5 = 11)

Approximately how much air mist be pumped down from the surface to fill a 60 litre container if the container was in 50 metres of water?

360 litres
(Using box method.. 60 x 6 = 360)

What is the partial pressure of  Nitrogen in Air if breathed up a mountain, where the surrounding pressure is 0.6 atm?

0.48 %
Even this can be worked out by the Box method!
the absolute pressure is 0.6 ( it says so in the question!)  the approximate percentage of Nitrogen in the air is .80%   so the calculation would be: 0.8 x 0.6 = 0.48)

A diver breathes from a cylinder that contains 0.03 % carbon monoxide. At a depth of 25 metres, this would have the same effect as breathing  … % at the surface?

0.105 %
(Using box method: 0.03 X 3.5 = 0.105)

At a depth of 20 metres, approximately how much denser is the air a diver breaths as compared to the surface?

3 times
(even this can by solved using box method: 1 x 3 = 3)

If a diver breathes a complete cylinder of air in 70 minutes.  at the surface, how long would it take to breathe the whole cylinder at 25 metres?

20 minutes
Using the box method: (70 divide by 3.5 = 20 minutes)

If an object weighs 720 Kg and displaced 120 litres, how much more fresh water would need to be displaced to bring the object to the surface?

600 litres

( as it’s in fresh water,   720 – 120 = 600 )

If an object weighs 377Kg and displaced 89 litres, how much more sea water would need to be displaced to bring the object to the surface?

277 litres

( as it’s in salt water,  377 divide by 1.03 = 366.
Then .. 366 – 89 = 277)

If a full scuba cylinder was placed outside in full sunshine on a hot day. What would happen to the pressure inside the cylinder?

The pressure inside the cylinder will increase

If an object that weighs 970 Kg and displaced 420 litres, is in fresh water how much air would need to be added to a lifting bag to bring the object to the surface?

550 litres
( as it’s in fresh water,  970 – 420 = 550)

If an object that weighs 68 Kg and displaced 15 litres, is in salt water how much air would need to be added to a lifting bag to bring the object to the surface?

51 litres

(as it’s in sea  water,  68 divide by 1.03 = 66
Then .. 66 – 15 = 51 litres)

If a fully inflated balloon was placed in a cold room, what would happen to the volume?

The volume of the Balloon would decrease