Ok, I have a test tommorow and I don't know how come mercury rises up to 76cm because of atmospheric pressure, what's the working(calculation). Help plz.
2006-12-03 16:04:21 · 4 answers · asked by Mike 4 in Science & Mathematics ➔ Physics
Pressure ( P ) is the ratio of the force ( F ) applied to a surface to the surface area ( A ).
P = F / A
A manometer is an device employed to measure pressure. There are a variety of manometer designs. A simple, common design is to seal a length of glass tubing and then bend the glass tube into a U-shape. The glass tube is then filled with a liquid, typically mercury, so that all trapped air is removed from the sealed end of the tube. The glass tube is then positioned with the curved region at the bottom. The mercury settles to the bottom.
After the mercury settles to the bottom of the manometer, a vacuum is produced in the sealed tube. The open tube is connected to the system whose pressure is being measured. In the sealed tube, there is no gas to exert a force on the mercury. In the tube connected to the system, the gas in the system exerts a force on the mercury. The net result is that the column of mercury in the left (sealed) tube is higher than that in the right (unsealed) tube. The difference in the heights of the columns of mercury is a measure of the pressure of gas in the system.
For example, the left column of mercury corresponds to 875 mm on the scale. The top of the right column of mercury corresponds to 115 mm. The difference in heights is 875 mm - 115 mm = 760. mm, which indicates that the pressure is 760. mm Hg (at sea level and standard temperature). This is also equal to 1atm.
(ATM) is intended to represent the mean sea level atmospheric pressure at the latitude of Paris, France, and as a practical matter, truly reflects the mean sea level pressure for many of the industrialized nations (those with latitudes similar to Paris).
2006-12-03 16:15:47 · answer #1 · answered by Griffin 2 · 1⤊ 0⤋
Because 76cm of mercury exerts the same pressure as the entire atmosphere (where only the height but not the volume matters). Mercury was chosen because of its density and the fact that it's conveniently liquid at standard temperature and pressure.
2006-12-03 16:13:06 · answer #2 · answered by hznfrst 6 · 1⤊ 0⤋
The rise of mercury has something to do with it's CHEMICAL PROPERTY, so it is constant as long as it is inside a vacuum tube. The pressure in the atmosphere make it rise. There's also a need for consideration for the DENSITY.
The truth is, we can use ALL kinds of liquid to determine pressure. But as the density of liquid increases, the column needed to make a vacuum tube also increases. The use mercury, perhaps, is a suggestion from Galileo Galilei, because he found out that it is significantly denser than water. To create a vacuum with water takes a column over 30 feet long, while with mercury it takes less than three feet.
And as for the formula, well... I dunno.
2006-12-03 16:27:38 · answer #3 · answered by Paw 3 · 0⤊ 1⤋
after 33mints
2006-12-03 16:43:16 · answer #4 · answered by wedad b 1 · 0⤊ 0⤋