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Density of the Best Laboratory Vacuum

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Zitzewitz, Paul & Robert Neff. Physics. New York: Glencoe, 1995: 267. "Standard Atmosphere
1 × 105 Pa
Best Vacuum
1 × 10−12 Pa"
1 × 10−20 g/cm3
>McAllister, Robert. McAllister Technical Services. Electronic Mail. 24 March 1997. "Pressures of 5 × 10−11 torr are not uncommon in everyday science labs" 8 × 10−17 g/cm3
Sears & Zemansky. University Physics, Complete Edition. Menlo Park, CA: Addison Wesley, 1962: 315, 694. "Density of air 1.29 × 10−3 g/cm3 at STP… pressures as low as 10−8 Pa" 1 × 10−16 g/cm3

A vacuum theoretically is a space devoid of matter. A vacuum is a volume from which practically all air has been exhausted. A perfect vacuum has never been made. In order to find the density of a laboratory vacuum, I needed to use the following ratio:

density of vacuum/density at STP = pressure of vacuum/pressure at STP

Where STP is standard temperature and pressure. The reason I needed to use the ratio was because a vacuum is usually measured by its pressure and not its density. The density of air at STP is 1.29 × 10−3 g/cm3 and the pressure of air at one standard atmosphere is 101,325 pascals. To find the density, I used a value for the vacuum pressure found in each source and plugged it into the formula. For example:

density of vacuum/1.29 × 10−3 g/cm3 = 10−12 Pa/ 105 Pa
density of vacuum = 1.29 × 10−20 g/cm3

Mesah Harwood -- 1999

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