Torricelli's Barometer Measures Pressure via Liquid Height in Vacuum

Steps:

• Atmospheric pressure pushes liquid up a closed tube partially filled with liquid.
• Vacuum above the liquid column allows the liquid to rise until balanced by its weight.
• Height h equals atmospheric pressure via P = ρgh, where ρ is density and g is gravity.
• Diagram with vacuum above h correctly shows this balance.

Why D is correct:

• Torricelli's principle defines the barometer as a vacuum-sealed tube where h directly equals P_atm / (ρg).

Why the others are wrong:

• A: Likely open tube; h measures hydrostatic pressure, not atmosphere.
• B: Possible air-filled space; compresses liquid, distorting h from true atmospheric value.
• C: Air above; partial pressure reduces effective h, misrepresenting full atmosphere.

Final answer: D