Quiz - Physics - Gauge Pressure

What is the gauge pressure at 16 metres/53 feet of fresh water?

  • a 2.55 ATM/37.59 psi

    Votes: 12 12.4%
  • b. 2.6 ATM/38.28 psi

    Votes: 13 13.4%
  • c. 1.55 ATM/22.89 psi

    Votes: 58 59.8%
  • d. 1.6 ATM/23.58 psi

    Votes: 14 14.4%

  • Total voters
    97

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No wonder people think I am an idiot. Just re read the question and noted the “fresh”.
After taking numerous electrical contractor tests for all the different states I've worked in, I have a tendency to read and reread the questions posed. Saved my butt more than a few times. Still remember some of the "trick" questions, but that's a post for another day.
 
Never having heard of "gauge pressure," I did not understand the question so responded with "a. 2.55 ATM" . Was surprised to see so many responses of (c), so Googled "gauge pressure", found a similar definition. Now I understand both the question and the answer.

This notion of zeroing out a gauge to atmospheric pressure seems a little bonkers to me -- climbing a hill or going into an airplane is not the same thing as entering a vacuum! I suppose it is highly pragmatic in some industries that deal with measuring pressures all the time, hence the terminology. Is that right, and if so, which are the relevant industries?

A lot of chemical engineering, and chemical manufacturing & similar industries, rely on controlling temperatures and pressures (and flows, in some instances). As a quick example, removal of solvents, or separation of mixtures via distillation: in general, boiling points of materials tend to decrease as the system pressure decreases, so, by pulling a vacuum on a system, the heat input required to remove water/solvent/whatever you're trying to purify also goes down. Now, if you've spent less energy creating the vacuum than you would have raising the temperature, you've saved energy, making your separation cost less.
 

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