Some air is trapped by a thread of mercury 85mm long in a small capillary tube .When the tube is held horizontally , the length of the air column is 10mm ;when it is held vertically with the closed and downwards, the length is 9mm .Find the atmospheric pressure.
（Take g=10 ms^-2 ; density of mercury= 14x10 ^3 kg m^-3 )
Mａｔｔｅｒ
2008-04-17 2:44 am
回答 (1)
2008-04-17 4:30 am
✔ 最佳答案
Let P be the atmospheric pressure (in mm Hg) When the tube is horizontal, the pressure of the trapped air is P
When the tube is vertical, the pressure of the trapped air becomes (P+85) mmHg
Applying Boyles Law:
P x 10 = (P+85) x 9
solving for P gives P = 765 mmHg
To change P into N/m2 (or Pa) give
atmospheric pressure = (765/1000)x14000x10 N/m2
= 107 100 N/m2
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