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| Pressure & its measurement |
Pressure
The perpendicular force exert on a unit area
is called pressure.
That is P = F/A
Explanation: The gas molecules always move continuously
and strike with wall or with each other and exerting a pressure on it. Such as
filling of tube or balloon.
Instrument used to measure the pressure
Different instruments are used to measure pressure.
One of them is barometer which is used to measure pressure which consist of a
glass tube filed with a mercury inverted in a dish of mercury.
Unit of pressure
As P = F/A where the force unit is “N” newton and area unit is meter “m”.
So the unit of pressure is NM – 2 which
is equal to one Pascal.
Some other common unit of pressure are as follow
1atm
(atmosphere) = 76 cm of Hg (mercury)
1atm
(atmosphere) = 760 mm of Hg (mercury)
1atm
(atmosphere) = 706 torr of Hg (mercury)
1atm (atmosphere) = 101253 Pascal
of Hg (mercury)
1atm
(atmosphere) = 1.01253 bar of Hg (mercury)
Instrument or devices to measure pressure
The two different instrument are as follow
Barometer
Manometer
Barometer
It is used to measure atmospheric pressure. It consist of a glass tube filled with a mercury inverted in a dish of mercury. The level of mercury falls due to gravity and stays at a particular height. The staying of mercury at a simple barometer at a certain height is due to atmospheric pressure which is exerted by air on mercury in a dish.
Designed
by
This apparatus was designed
by an Italian scientist Evangelista Torricelli. Evangelista Torricelli was an Italian physicist and mathematician,
best known for his invention of the barometer.
Born: Evangelista Torricelli born in October 15, 1608, Faenza,
Italy
Died: Evangelista Torricelli died on October 25, 1647, Florence,
Italy
Manometer
It is also used to measure pressure of gases
and liquids in laboratory.
Designed
by
It was designed by Otto von
Guericke. He was a German scientist, inventor and politician. Evangelista Torricelli
Born: Otto von Guericke born in November 20, 1602, Magdeburg,
Germany
Died: Otto von Guericke died on May 21, 1686, Hamburg,
Germany
Density
The
mass per unit volume of any substance is called density.
d = m/v
Explanation:
If the
intermolecular forces of a substance is high then density will be high that why
solid has high density than liquid and gases.
Intermolecular
forces α to density
Density also depends on
temperature. As the temperature increases the density will decreases.
Density α 1 / temperature
Unit of density
As density d = m/v
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