Approximate vacuum achievable at Calgary's altitude?

Approximate vacuum achievable at Calgary's altitude?

• A. 40 in Hg
• B. 15 in Hg
• C. 5 in Hg
• D. 26.5 in Hg

Answer: (D)

Altitude lowers atmospheric pressure, so the ambient pressure you’re working against isn’t the sea-level value of 29.92 inHg. At Calgary’s elevation (about 1,000 m), the standard atmospheric pressure is roughly 89 kPa, which converts to about 26.5 inHg. That means the approximate vacuum you can achieve in that location (the pressure of the surrounding air you must evacuate against) is around 26.5 inHg. The other numbers don’t fit because they would require a pressure higher than the local ambient or far lower than what the local air pressure allows. 40 inHg would exceed Calgary’s ambient pressure, while 15 or 5 inHg would imply a much stronger vacuum than the surrounding air would permit in that setting.

Altitude lowers atmospheric pressure, so the ambient pressure you’re working against isn’t the sea-level value of 29.92 inHg. At Calgary’s elevation (about 1,000 m), the standard atmospheric pressure is roughly 89 kPa, which converts to about 26.5 inHg. That means the approximate vacuum you can achieve in that location (the pressure of the surrounding air you must evacuate against) is around 26.5 inHg.

The other numbers don’t fit because they would require a pressure higher than the local ambient or far lower than what the local air pressure allows. 40 inHg would exceed Calgary’s ambient pressure, while 15 or 5 inHg would imply a much stronger vacuum than the surrounding air would permit in that setting.