🔍 Key Concepts

• This is a bubbler-type tank level measuring system: air is forced down tube E and bubbles out at point D under the liquid surface. • The pressure at point D depends on the depth of liquid H above D (hydrostatic pressure). • In a gauge like column C, the height of the indicating column depends on the pressure applied to it.

💭 Think About

• Look at where point D is located and how far below the liquid surface it is. What physical quantity does that depth create at D? • How does a pressure gauge or manometer work: what is the relationship between the applied pressure and the height of the fluid column that it shows? • Is the column showing the actual tank liquid height, or is it responding to some other variable that, in turn, depends on that height?

✅ Before You Answer

• Confirm that air pressure at B is adjusted only high enough to overcome the liquid head and produce steady bubbles at D. • Identify that the pressure in the line going to column C is the same as the pressure at D (neglecting small losses). • Recall that in a manometer, fluid column height is proportional to applied pressure, not equal to the pressure itself.