The tendency of light to bend as it passes through objects with different densities is called what? This causes objects viewed underwater to appear what?

Refraction — larger or closer. Light bends as it passes through water, the mask glass, and the air inside the mask, causing objects to appear approximately 25% larger and closer than they actually are.

A diver breathes through 100 bar in 30 minutes at 30 metres. How much will they breathe through in 15 minutes at 20 metres?

37.5 bar. Time halves so halve the consumption: 100 ÷ 2 = 50 bar. Find surface equivalent: 50 ÷ 4 ata = 12.5 bar. Multiply by pressure at 20 m (3 ata): 12.5 × 3 = 37.5 bar.

A diver has a volume of 80 litres and weighs 70 kg. How much weight do they need for neutral buoyancy in salt water?

Approximately 12 kg. Salt water displaced: 80 × 1.03 = 82.4 kg. Subtract diver weight: 82.4 − 70 = 12.4 kg.

What happens to gas dissolved in water when pressure is increased to 4 ata? (Henry's Law)

The amount of gas dissolved increases. Henry's Law states that gas solubility in a liquid is directly proportional to the partial pressure of that gas.

A diver weighs 100 kg and has a volume of 85 litres. What is the minimum BCD lift required for neutral buoyancy in salt water?

12.09 litres. Convert kg to litres: 100 ÷ 1.03 = 97.09 L. Subtract diver volume: 97.09 − 85 = 12.09 L.

At what depth does breathing air become potentially toxic due to oxygen partial pressure?

Approximately 66 metres. Maximum safe PPO2 is 1.6 ata. Calculation: 1.6 ÷ 0.21 = 7.619 ata. Depth: (7.619 − 1) × 10 = 66.19 m.

A scuba tank is moved from a cool room into direct sunlight. What happens? (Charles' Law)

The pressure increases and the volume remains the same. The tank is rigid and cannot expand, so rising temperature causes pressure to rise instead.

A balloon with a volume of 0.8 L is released from 85 metres. What is its volume at the surface? (Boyle's Law)

7.6 litres. Pressure at 85 m is 9.5 ata. Balloons get bigger as they ascend, so multiply: 9.5 × 0.8 = 7.6 L.

A scuba tank has 3,000 psi at the surface. What are the pressure and volume at 30 metres?

They are the same. A rigid scuba tank does not transfer external water pressure to the gas inside, so both pressure and volume of the contents remain unchanged at depth.

Because water is denser and more elastic than air, how does sound behave underwater?

Sound travels approximately 4 times faster in water than in air — around 1,500 m/s versus 340 m/s. As a result, divers cannot determine the direction a sound is coming from.

Test your knowledge with practice 12 questions exams that are similar to the exam you will do at the PADI IE.

Dive Physics — Final Exam

Refraction • Gas consumption • Buoyancy • Henry's Law • BCD lift • Altitude • O² toxicity • Charles' Law • Boyle's Law • Sound