Finding temperature through a manometer

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SUMMARY

The discussion focuses on calculating temperature using a mercury manometer in a gas cell scenario. The initial mercury height is 120 mm at 0°C in an ice-water mixture, dropping to 30 mm in an industrial freezer. The user initially assumed constant pressure but later recognized that pressure changes while volume remains constant. The relevant equation for this scenario is p1*v1/t1 = p2*v2/t2, which is crucial for determining the unknown temperature.

PREREQUISITES
  • Understanding of gas laws, specifically the ideal gas law.
  • Familiarity with manometer principles and fluid mechanics.
  • Knowledge of temperature conversion between Celsius and Kelvin.
  • Ability to manipulate algebraic equations involving multiple variables.
NEXT STEPS
  • Study the ideal gas law and its applications in thermodynamics.
  • Learn about the principles of manometry and how to interpret manometer readings.
  • Explore temperature conversion techniques, particularly between Celsius and Kelvin.
  • Investigate how pressure variations affect gas volume and temperature relationships.
USEFUL FOR

Students studying physics or engineering, particularly those focusing on thermodynamics and fluid mechanics, as well as anyone needing to understand manometer applications in real-world scenarios.

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Homework Statement


The mercury manometer shown in the figure is attached to a gas cell. The mercury height h is 120 mm when the cell is placed in an ice-water mixture. The mercury height drops to 30 mm when the device is carried into an industrial freezer. HINT: The right tube of the manometer is much narrower than the left tube. What reasonable assumption can you make about the gas volume?
[PLAIN]http://img36.imageshack.us/img36/6331/knightfigure1650.jpg
I'm assuming the temperature is originally at 0C since it says it's in an ice-water mixture. I'm also assuming pressure is constant throughout the problem.

Homework Equations


V/T=V/T
C+273=K

The Attempt at a Solution


I attempted to do:
120/273K = 90/T
T=-68.25C
Wrong answer. I'm guessing there's more to put into the volume part of the equation than just the height, but I don't know exactly what. Can anyone help? Thanks.
 
Last edited by a moderator:
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After much observation, I was wrong to conclude pressure would be the same. After reading the hint carefully, I came to the conclusion pressure changes, while volume remains constant. Still, I don't know how to find the pressure of the system.
 
p1*v1/t1=p2*v2/t2
 
Last edited:

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