MeasuringAbsoluteZero

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course Phy 202

1/19 4

Measuring absolute zeroDuring the first hour of class we used the bottles as we did on the first day.  This time I measured the temperature of the air in one bottle as it sat outside, then after it was brought in and allowed to sit for a time in the room.  We found that its temperature rose from 6 Celsius to 22 Celsius.  Water rose in the tubes of the various bottles to heights between 35 cm and 65 cm.

The pressure in the bottle was originally 1 atmosphere, which we will assume to have been 100 000 Pa.  So one point on a pressure vs. temperature graph would be (6 Celsius, 100 000 Pa).

Assuming the 'low' estimate of a 35 cm water column, what would be the coordinates of the point on this graph corresponding to temperature 22 Celsius?  (start by figuring out how much the pressure had to rise to support a 35 cm column of water).

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1.53atm

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I don't think this is consistent with the points on the graph.

One point is (6 Celsius, 100 000 Pa).

The 35 cm column of water corresponds to an increase in pressure of 3500 Pa, since each cm requires an additional pressure of 100 Pa.

So the pressure in the bottle is 3500 Pa higher than the original 100 000 Pa pressure of the atmosphere.

The coordinates of the second point are therefore (22 Celsius, 103 500 Pa).

Now on a graph of pressure vs. temperature, at what point does the line through these two points intersect the temperature axis?

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Plot these two points on a graph of pressure vs. temperature.  Sketch the line through these points and extend it until it reaches the point where the pressure coordinate is zero.  What is the temperature coordinate at that point? 

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The pressure is about 0.75 at 0C and the temp is -20C at 0 pressure.

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This is your estimate for the 'low' value of the height of the water column.

Repeat assuming the 'high' estimate of 65 cm for water column height.

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35C and 2atms

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Repeat once more, using your measured height.

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That was the measured height.

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