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Homework Help: Mercury Monometer, Pressure, Temperature

  1. Feb 8, 2010 #1
    1. The problem statement, all variables and given/known data

    A mercury manometer is attached to a gas cell (this is the closed end). The mercury height is 120mm when the cell is placed in an ice-water mixture. The mercury height drops to 30mm when the device is carried into an industrial freezer. What is the temperature of the freezer?

    2. Relevant equations

    pressure = (density, d)(height of mercury, h)(gravity, g)
    P1V1/T1 = P2V2/T2

    3. The attempt at a solution

    Right off the bat, I know the answer is -27.9 degrees Celsius. Since the tube containing the mercury is much more narrow than the actual gas cell, I neglected any change in volume and I'm left with P1/T1=P2/T2, which manipulates to P1/P2=T1/T2. I subbed the pressure = dhg into P1/P2. Density and gravity will cancel out and I'm left with T1/T2=h1/h2. Following this, I get 120mm/30mm = 4 and then I just solve for T1. I have always got -68.3 degrees Celsius. Where am I going wrong?
  2. jcsd
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