Another one Kourtney😝💕 — let's solve it.
10. The figure below shows a water U-tube manometer used to measure the gas pressure of a gas cylinder.
Step 1: Convert the density of the liquid to SI units.
ρ=0.8g/cm3=0.8×1000g1kg×(1m100cm)3=0.8×1000kg/m3=800kg/m3
Step 2: Determine the height difference of the liquid columns and convert to meters.
The liquid level at X is 9 cm below the tap. The liquid level at Y is 9 cm above the level Z (which is at the same horizontal level as X).
The total height difference h is the sum of these two displacements.
h=9cm+9cm=18cm
h=0.18m
Step 3: Calculate the pressure due to the liquid column difference.
Assume the acceleration due to gravity g=10m/s2.
Pliquid=ρgh
Pliquid=800kg/m3×10m/s2×0.18m
Pliquid=1440Pa
Step 4: Calculate the gas pressure in N/m2 (Pascals).
Since the liquid level in the arm connected to the gas supply (X) is lower than the level in the arm open to the atmosphere (Y), the gas pressure is greater than the atmospheric pressure.
Pgas=Patm+Pliquid
Pgas=101400Pa+1440Pa
Pgas=102840 Pa
Step 5: Convert the gas pressure to cmHg.
To convert pressure to the height of a mercury column, use the formula P=ρHgghHg. The density of mercury (ρHg) is 13600kg/m3.
hHg=ρHggPgas