A depth equivalent to one atmosphere of pressure in seawater is equal to what depths in seawater and freshwater, respectively?

A depth equivalent to one atmosphere of pressure in seawater is equal to what depths in seawater and freshwater, respectively?

• A. 9 m (30 feet) ; 9.5 m (31 feet)
• B. 10 m (33 feet) ; 10.4 m (34 feet)
• C. 12 m (39 feet) ; 12.5 m (41 feet)
• D. 11 m (36 feet) ; 11.5 m (38 feet)

Answer: (B)

When measuring the pressure caused by a column of water, the hydrostatic pressure increases with depth. About one atmosphere of extra pressure from the water column is reached at roughly 10 meters in seawater because seawater is denser, so ρ g h grows more quickly with depth. In freshwater, the density is a bit lower, so the same pressure comes from a slightly greater depth—about 10.3 to 10.4 meters. Therefore, the depth that gives one atmosphere of hydrostatic pressure is around 10 m in seawater and about 10.4 m in freshwater (roughly 33 ft and 34 ft). The listed values align with these approximate relationships, making that choice the best match.

When measuring the pressure caused by a column of water, the hydrostatic pressure increases with depth. About one atmosphere of extra pressure from the water column is reached at roughly 10 meters in seawater because seawater is denser, so ρ g h grows more quickly with depth. In freshwater, the density is a bit lower, so the same pressure comes from a slightly greater depth—about 10.3 to 10.4 meters. Therefore, the depth that gives one atmosphere of hydrostatic pressure is around 10 m in seawater and about 10.4 m in freshwater (roughly 33 ft and 34 ft). The listed values align with these approximate relationships, making that choice the best match.