In hydrostatic level measurement, pressure at the bottom is proportional to which product?

• A. Height and viscosity
• B. Temperature and density
• C. Specific gravity and height
• D. Flow rate and area

Answer: (C)

In hydrostatic level measurement, the pressure at the bottom of a liquid column depends only on how tall the column is and how dense the liquid is. For a stationary fluid, pressure is P = ρ g h, where ρ is the liquid density, g is gravity, and h is the height of the liquid. This can also be written as P = γ h, with γ being the weight density (γ = ρ g). Specific gravity expresses density relative to water, so ρ = SG × ρ_water and γ = SG × γ_water. Therefore, bottom pressure is proportional to the product of height and (specific) density. Viscosity doesn’t affect this static pressure, and temperature, flow rate, or cross-sectional area don’t enter the hydrostatic relation in this context.