PADI Divemaster Certification Practice Exam

What happens to a cylinder after releasing all the air from it?

1. It heats up

2. It cools down

3. It expands

4. It contracts

The correct answer is: It cools down

When all the air is released from a cylinder, the temperature of the gas inside the cylinder drops, resulting in a cooling effect. This phenomenon occurs due to the principles of thermodynamics, specifically related to the Joule-Thomson effect. As the gas expands rapidly when it is released from the high-pressure environment of the cylinder to the lower pressure outside, the kinetic energy of the gas molecules decreases, which leads to a reduction in temperature. This cooling can be readily observed in applications such as when using aerosol cans or when gas cylinders are emptied quickly. The transition from high pressure to lower pressure causes the gas molecules to spread out and lose energy, contributing to that cooling effect. Understanding this concept is essential for safe handling and efficient use of compressed gas systems.