Scuba Diving Physics and Physiology of Diving 3

Question 1

Why does sound travel approximately 4 times faster underwater than in air?

Accepted Answer

Water is denser and less compressible, transmitting pressure waves more efficiently

Answer

Sound speed depends on a medium's elasticity and density; water's high bulk modulus (stiffness) enables sound to travel at ~1,500 m/s versus ~340 m/s in air.

Question 2

A thermocline is best described as:

Accepted Answer

A distinct boundary layer where water temperature changes sharply with depth

Answer

A thermocline is a layer where warm surface water meets colder deep water, creating a steep temperature gradient that can affect buoyancy and visibility for divers.

Question 3

Which color of light is absorbed first and most rapidly as depth increases in the ocean?

Accepted Answer

Red

Answer

Red wavelengths have low energy and are absorbed within the first few meters of water, which is why red objects appear gray or black at depth without an artificial light source.

Question 4

What does the no-decompression limit (NDL) on a dive computer represent?

Accepted Answer

The maximum time a diver can stay at a given depth before requiring a decompression stop to ascend safely

Answer

The NDL is the time limit at a specific depth within which the diver has absorbed enough nitrogen to ascend directly to the surface safely without mandatory decompression stops.

Question 5

What physical phenomenon explains why objects underwater appear approximately 25% larger and 25% closer than they actually are?

Accepted Answer

Refraction of light at the water-mask air interface bends light rays toward the eye

Answer

Light refracts (bends) as it passes from water into the air space inside the mask, creating a virtual image that appears roughly 25% larger and closer than reality.

Scuba Diving Practice Test

Scuba Diving Practice Test

Scuba Diving Physics and Physiology of Diving 3