PADI Divemaster Certification Practice Exam

What happens to the density of a gas as depth increases?

1. It decreases

2. It stays the same

3. It becomes half

4. It doubles

The correct answer is: It doubles

When considering the behavior of gases under pressure, it is important to understand the relationship between gas density and depth in a medium, usually water. As the depth increases, such as when diving underwater, the pressure surrounding a gas also increases. The density of a gas is defined as its mass divided by its volume. When pressure increases (as it does with increasing depth), gases compress, meaning the same mass of gas occupies a smaller volume. This results in an increase in density. At depths of 10 meters of seawater, for example, the pressure increases by about 1 atmosphere, which can cause the density of gases to become significantly greater than at the surface. While the exact doubling or specific change can depend on factors such as temperature and the specific gas involved, it is generally true that the density of a gas increases as depth increases due to the increasing ambient pressure. Typically, under controlled conditions, our understanding can lead to a simplification that captures the significant increase in density. The assertion that the density doubles at certain depths reflects a fundamental understanding of how gases react under pressure, although exact ratios may vary based on specific circumstances and gas laws. In the context of this examination, it encapsulates the principle that density increases significantly with depth