Question

What if the water levels were not equal? Calculate the pressure inside Pipet A if the height of the water is 14.2 mm higher than the water in Pipet B. The atmospheric pressure is 760.2 mm Hg. Be sure to consider the difference in units: 1mmH20 does not equal 1 mm Hg. Start by converting the height pressure difference from mm H20 to mm Hg. You will find the following formula for pressure useful for the unit conversion. P=dxgxh

Answer 1

"Gauge Pressure" due to a fluid of density 'd' at depth 'h' in gravitational field 'g' is h*d*g

Now pressure due to 1 mm of H₂O is approximately equal to 0.073556 mm of Hg.

Hence, pressure due to 14.2 mm of H₂O is equal to 14.2 * 0.073556 mm of Hg.

Hence, gauge pressure of 14.2 mm of H₂O is 1.0444952 mm of Hg.

Now, as per question, 1 atm = 760.2 mm of Hg.

Hence, Pressure due to 14.2 mm of H₂O = 1.0444952 mm of Hg = (1/760.2) * 1.0444952 = 1.3739 * 10^-3 atm.

Note that this is the gauge pressure at height of 14.2 mm of Water.