November 11, 2011 Posted by Admin

Barometer vs Manometer  

Barometer and manometer are used to measure pressures. They are simple instruments, which are based on the same principle. However, the occasions where they are being used are different. Today, there are many sophisticated equipments to replace the old barometers and manometers, and they are more user friendly, fast and reliable.  

What is Barometer?

Barometer is an instrument that measures the air pressure. This instrument is more helpful in weather forecasting based on the atmospheric changes. Pressure can be easily used for weather forecasting, because weather patterns are carried around in regions of high and low pressure. There are two types of barometers as mercury barometer and Aneroid Barometer. Mercury barometer is widely used, and it is more reliable. Aneroid barometer is the newer version of the barometer, which is digital. The first barometer, which was constructed using mercury, was invented by Evangelista Torricelli in 1643. Mercury barometer consists of a tall (about 3 feet) tube, which is filled with mercury. This tube is inverted in a mercury-filled container (which is known as a reservoir), so that the sealed end of the tube has a vacuum. The height of the mercury column inside the glass tube will change according to the atmospheric pressure. Because of this change, the pressure exerted by the mercury column will be equal to the pressure exerted by the atmosphere on the surface of the mercury reservoir. For example, if the atmospheric pressure is higher than the pressure exerted by the mercury column, the mercury level inside the tube will rise.  If the atmospheric pressure is lower than the weight of the mercury column, the level will fall. Modern barometers use electrical equipments to measure the air pressure changes than using mercury barometers. They use electrical charges and predict more accurate weather changes. The aneroid barometer was invented by Lucien Vidie in 19th century. It uses a cell, which expands or contracts depending on the air pressure.  In barometers, decrease in the pressure indicates rain and windy weather. An increasing pressure indicates dry, colder weather. A slow, and sustained rise in the pressure foresees a long period of good weather.

What is Manometer?

Manometer is a device, which can be used to measure pressure. It is an equipment consisting of a “ U” shaped tube with thin arms. The tube is open to the air in both sides, and it is filled with liquid. Usually it is filled with mercury because of its high density. The height difference between the liquid in two arms is measured, and from it, the pressure difference can be calculated.

Pressure (P) = ρ g h       

Where, ρ = density; g = acceleration of gravity (9.81 m/s2); h = liquid height 

What is the difference between Barometer and Manometer?

• Barometer is a type of close-end manometer.

• Barometer is specially designed to measure the atmospheric pressure, whereas manometer can also be used to measure the pressures, which are lower than atmospheric pressure.

• In a manometer, both ends of the tube are open to outside (some may have a one closed end), whereas in the barometer one end of the glass tube is sealed and it contains a vacuum. 

Filed Under: Physics Tagged With: aneroid barometer, Barometer, barometer vs, barometers, barometers vs, manometer, manometer vs, manometers, manometers vs, measure pressure, measuring air pressure, mercury barometer