Pressure Law - question about experiment apparatus

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SUMMARY

The discussion focuses on the apparatus used to verify the Pressure Law, which states that pressure is directly proportional to temperature for a fixed mass and volume of gas. A key point raised is the importance of using a short length of rubber tubing to connect the flask to the pressure gauge. The longer tubing introduces a volume of air that is not accounted for in the experiment, leading to inaccurate pressure readings due to poor heat conduction and density differences. Participants confirmed that the air in the tubing cools before reaching the gauge, further impacting measurement accuracy.

PREREQUISITES
  • Understanding of the Pressure Law in thermodynamics
  • Familiarity with gas laws and their applications
  • Knowledge of heat conduction principles
  • Experience with experimental apparatus setup in physics
NEXT STEPS
  • Research the implications of gas density on pressure measurements
  • Study the effects of thermal conductivity in experimental setups
  • Explore alternative materials for tubing in pressure experiments
  • Learn about calibration techniques for pressure gauges
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This discussion is beneficial for physics students, laboratory technicians, and educators involved in teaching thermodynamics and experimental physics, particularly those focusing on gas laws and pressure measurement accuracy.

slakedlime
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[SOLVED] Pressure Law - question about experiment apparatus

pressurelaw.jpg

Introduction
Above is a diagram representing the apparatus which can be used to perform the experiment which verifies the Pressure Law (i.e. pressure is directly proportional to temperature for a fixed mass and volume of gas).


The question
Why is it important to use a short length of rubber tubing to connect the flask to the pressure gauge?


The attempt at a solution Here is my hypothesis:
The rubber tubing contains a volume of air which is not accounted for in the experiment (the volume of air being restricted only to that in the flask). Air is a poor conductor of heat energy so the air in the tubing is not uniformly heated when the air in the flask is. The air in the tubing is denser than that in the flask. Thus when the flask is heated, the actual volume of the air decreases as some escapes into the tube. Consequently, a wrong pressure reading is given.

Could someone please verify this? Thank-you very much, in advance. :smile:
 
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Correct - there is also the effect of the air cooling down a long tube before it reaches the pressure gauge
 
Last edited:
Thank you for your help and input. :smile:
 

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