Question

A mercury barometer has a cylindrical capillary tube of radius inverted vertically on the mercury in the trough. Atmospheric pressure is 76 cm of mercury but the level of mercury in the capillary is 75cm. The portion of the tube without mercury is 10cm in length. Considering that this region is occupied by ideal gasses, the number of moles of the ideal gas will be :

[Given : Density of mercury = 13.6 g/cc, surface tension of mercury = 0.5 N/m, temperature = 37°C, g = 10 m/s2, universal gas constant = R, angle of contact of mercury on tube = 135°]

Answer 1

Explanation:

Since the mercury rises only 50cm it implies the rest of the excess atmospheric pressure is being countered by the pressure at the top of the tube.

So pressure at top=atmospheric pressure - 50cm of Hg=(75−50)cm=25cm of Hg=1/3×100kPa=33.33kPa