Physics Help Forum Setup investigating V‧T relationship

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 Aug 30th 2008, 08:49 PM #1 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 Setup investigating V‧T relationship The setup investigating the relationship which is then defined as the Charles Law. We have to keep the mass and pressure constant. It is easy to keep mass constant inside a closed container. I found a setup having thermometer and a capillary tube. I guess it is the capillary tube which makes the pressure constant, right? If I was wrong, please tell me how pressure is kept constant as I thought pressure is only something with force over area which is really abstract and difficult to be seen
Aug 31st 2008, 10:33 AM   #2

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 Originally Posted by werehk The setup investigating the relationship which is then defined as the Charles Law. We have to keep the mass and pressure constant. It is easy to keep mass constant inside a closed container. I found a setup having thermometer and a capillary tube. I guess it is the capillary tube which makes the pressure constant, right? If I was wrong, please tell me how pressure is kept constant as I thought pressure is only something with force over area which is really abstract and difficult to be seen
You'd better describe the equipment or provide a diagram. There are a variety of experimental setups to verify Charles' Law. But as a first approximation I'd say that we need either an expanding volume (as in a balloon) or some way to "bleed" the excess pressure off to another chamber, so I'd say you are correct.

-Dan
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 Sep 1st 2008, 08:49 PM #3 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 With a stand hanging a thermometer which is partly immersed into a beaker of ice-water mixture. With bunsen burner heating the bottom part of the beaker. There exists a capillary tube which is attached to the thermometer which is also partly immersed into the ice-water mixture.In the diagram of my book, it points at the bottom of the thermometer labelled as "gas column" which I guess is a part of thermometer.( This is the best that I could describe) Is it the capillary tube in some way that helps to tell a constant pressure?
Sep 2nd 2008, 03:44 PM   #4

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 Originally Posted by werehk With a stand hanging a thermometer which is partly immersed into a beaker of ice-water mixture. With bunsen burner heating the bottom part of the beaker. There exists a capillary tube which is attached to the thermometer which is also partly immersed into the ice-water mixture.In the diagram of my book, it points at the bottom of the thermometer labelled as "gas column" which I guess is a part of thermometer.( This is the best that I could describe) Is it the capillary tube in some way that helps to tell a constant pressure?
If I've got the picture right, then yes. The capillary exists as a "slow bleed" for the excess pressure. We need a slow outlet for the pressure because any gas that leaves the system will screw up the experiment. So if we have a "slow enough" leak of gas we will still get fairly accurate results. As I understand it this kind of trade off is common to experiments in Thermodynamics.

-Dan
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