Answer to Question #99454 in Classical Mechanics for Omale

Question

What is the guage pressure of the gas in the closed tube in the figure? Take the atmospheric pressure to be 76cm hg

Answer 1

Gauge pressure is our only system pressure where we taking the atmospheric pressure is 0

It is the difference between the mercury level in both limbs of manometer.

At left limb above the horizontal line, P_gas is the pressure of gas

At right limb above the horizontal line, P_mercury is the pressure due to mercury

At equilibrium pressure at both limbs above the horizontal line are equal

Thus Gauge pressure due to gas = P_mercury is the pressure due to mercury

Lets assume the height of mercury above the horizontal line is 20cm

Then Thus Gauge pressure due to gas in closed vessel = 20cm Hg