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Homework Help: Measuring pressure using a manometer.

  1. Aug 2, 2013 #1
    1. The pressure of a gas cell is measured with a mercurcy manometer. The mercury is 32.6 cm higher in the outside arm than in the arm connected to the gas cell. Calculate the gas pressure.

    Relevant equations/given data
    2. p(Pressure at depth h) = p(Pressure of atmosphere) + ρ(Density of liquid)*g(Gravitionational acceleration)*h
    Pressure of atmosphere = 1atm = 101,300Pa. Density of mercury = 13,600kg/m^3

    Attempted solution
    3. p(gas) = p(Pressure of atmosphere) + ρ(Density of liquid)*g(Gravitionational acceleration)*h
    p(gas) = 101,300 + (13600*9.8*0.326) = 144749.28Pa = 144.75kPa. I have the solution and it says the answer should be 149.5kPa. Have I done something wrong, or is the solution incorrect?
  2. jcsd
  3. Aug 3, 2013 #2
    Your calculation is exactly correct. The answer is the book is for a mercury height of 36.2cm. Is there any chance that you misread the problem and got the 6 and 2 backwards? If not, don't spend any more time thinking about it, you know what you are doing and the answer key had a typo.

    Dr Peter Vaughan
    BASIS Peoria Physics
  4. Aug 3, 2013 #3
    Oh my!!! Stupid me! You are right, I misread the 6 and the 2 backwards. That clears it up, thanks for the help! =D
  5. Aug 3, 2013 #4
    Those are absolutely the most difficult mistakes to find. Fortunately, they are also by far the least important mistakes.
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