PADI Divemaster Certification Practice Exam

How does the volume of a balloon change as it rises from 20 meters to the surface?

1. It doubles

2. It remains the same

3. It triples

4. It quadruples

The correct answer is: It triples

The volume of a balloon changes as it rises from a depth of 20 meters to the surface due to the decrease in water pressure surrounding it. According to Boyle's Law, which states that for a given mass of gas at constant temperature, the volume is inversely proportional to the pressure, as the balloon ascends, the pressure decreases. Consequently, this drop in pressure allows the gas inside the balloon to expand, increasing its volume. At a depth of 20 meters, the pressure is approximately 3 atmospheres (1 atmosphere of air pressure at the surface plus an additional 2 atmospheres from the water column). As the balloon rises to the surface where the pressure is 1 atmosphere, the reduction in pressure causes the balloon's volume to increase as it seeks to balance the internal and external pressures. In this scenario, if the volume of the balloon at 20 meters is considered, as the pressure drops significantly upon ascent, the balloon can expand to around three times its original volume, making it three times larger as it reaches the surface. This illustrates the concept that gases will expand when external pressure decreases, leading to the conclusion that the correct answer reflects the volume tripling during the ascent.