HOW ATMOSPHERIC PRESSURE IS MEASURED ,WHAT IS ATMOSPHERIC PRESSURE AND HOW ATMOSPHERIC PRESSURE VARIES WITH ALTITUDE....

                       ATMOSPHERIC PRESSURE The force exerted by air due to its specific  weight on any surface is termed as atmospheric pre...

                      

ATMOSPHERIC PRESSURE

The force exerted by air due to its specific  weight on any surface is termed as atmospheric pressure,how ever the atmospheric pressure varies with respect to different location,the standard atmospheric pressure is measured by taking sea level as reference.

HOW ATMOSPHERIC PRESSURE VARIES WITH  ALTITUDE

we know that pressure(P)= normal force(F)/Area(A)

                      P=mass(m)*acceleration due to gravity(g)/area(A)     ( F=m*a)

                      P= Density(ρ)*volume(V)*g/A    {Density (ρ)=mass(m)/volume(V)}

                      P=ρ*g*(meter cube)/(meter square)

                      P=ρ*g*h             (h= vertical height ,ρ*g= specific weight)

From  the above equation its clearly seen that as the height from sea level increase or decrease  the value of pressure also increase or decrease accordingly .That is  the reason pressure  low at high altitude area like mountains and hills.

HOW ATMOSPHERIC PRESSURE IS MEASURED

*The device used to measure atmospheric pressure is known as barometer , so the atmospheric pressure is also known as barometric pressure.

*In this process a container and a glass tube is taken which are filled with mercury.

*Then the tube containing mercury  is dipped into the the container, In this case the cohesive force  is higher than the adhesive force which create non wetting effect for which the mercury fall in the tube however the level of mercury in the glass tube is higher than the level of the mercury  in the container.

*Due to fall of mercury level on the glass tube vacuum is created , as the pressure drops the saturation temperature of mercury also drops ,so the mercury start to vaporize , and exert vapor pressure on the surface of the mercury. 

*Pressure at point A= Atmospheric pressure

*Pressure at point B=ρ*g*h+ Vapor pressure

*Pressure at point A = Pressure at point B ( Because both point lies on the same level )

so Atmospheric pressure=ρ*g*h+Vapor pressure

 Atmospheric pressure=ρ*g*h   ( As the vapor pressure of mercury is too low so it taken as zero, for this reason mercury is used to measure atmospheric pressure)

Atmospheric pressure = 13600( kg/meter cube)*9.81(meter/sec square)*.76(meter)

Atmospheric pressure= 101.325 kpa/ 760 mm of  mercury 

In this way atmospheric pressure is measured.