Barometer | aneroid barometer

Barometer is used to measure the air pressure in a certain atmosphere. Pressure trends can predict short-term changes in weather. When the barometric reading drops suddenly, there is a possibility of a thunderstorm. When the barometric reading falls slowly, there is a possibility of rain. The day is likely to be clear when the barometric reading gradually rises. Barometer invented Italian scientist Evan Gelista Torricelli in 1643. The barometer measures atmospheric pressure using water air or mercury. The barometer works by balancing the weight of mercury in the tube against the atmospheric pressure. If the weight of the mercury is less than the pressure, then the mercury in the tube rises .if the pressure is more ,the mercury level falls inside the tube.


Barometer working |working principle of barometer

Barometer, working principle of balancing the weight of mercury in the tube against the atmospheric pressure like as set scales. If mercury is filled in a 1 meter long, thick walled glass tube closed at one end and open at the other end, it is made to stand vertically by turning it upside down in a tub full of mercury, then the mercury in the tube comes down and stops at a position. The height of the column of mercury in the tube is directly proportional to the atmospheric pressure, that is, as the atmospheric pressure increases, the mercury in the tube will be higher and vice versa. Generally this height is equal to 76 cm of mercury at sea level and it decreases as one goes up. It is called a barometer. That is why it is said that atmospheric pressure is equal to 76 centimetre column of mercury. A column of this height expresses a pressure equal to 1.013 bar. In this, other liquids can also be used in place of mercury, but with decreasing density, the length of the tube will have to be increased. For example, if water is used in place of mercury, the length of the tube will have to be kept at least 10.33 meters.

Types of barometer | Barometer types

  1. Mercury Barometer

Mercury Barometer is used to mercury, to measure atmospheric pressure . In ordinary barometers, there is a glass tube with one end closed and the other end open. Another vessel is taken in which some The mercury is filled up to a height, this glass tube is placed upside down in the vessel so that the open end comes in contact with the surface of the mercury in the vessel. By keeping this way, the level of mercury in the tube decreases somewhat and it starts falling down and stops at a certain height. The pressure of mercury from the bottom of the vessel to the height of the mercury in the tube is equal to the atmospheric pressure.

Advantage of mercury barometer:-

  1. In this type, mercury has low vapor pressure and very high density.
  2. Their surface is shining and opaque.
  3. It neither gets wet nor stick to the glass.
  4. Its evaporation rate is not very high.

Disadvantage of mercury barometer:-

  1. The probability of failure of the glass tube is very high.
  2. it is heavy in nature.     


  1. Aneroid Barometer :-

It is very important to know how to use a aneroid barometer, as meteorologists are sensitive to the weather. Before the change in climatic conditions, the pressure to change the readings begins. By tracking this change, you can prepare in advance. An aneroid barometer is a  device which is  used for measuring air pressure (atmospheric pressure) .in this  method does not involve  liquid for measuring atmospheric pressure .it is Invented in 1844 by French scientist Lucien Vidi  , it has flexible metal box which is known as an aneroid cell   and it is made from an  alloy of beryllium   and copper . usually several capsules, stacked to add up their movements is prevented from collapsing by a strong spring. The cell becomes expand or contract due to small changes in external air pressure cause . This expansion and contraction moves or drives mechanical levers such that the small movements of the capsule are amplified and displayed on the face of the aneroid barometer. Many models include a manually set needle which is used to mark the current position so that the change can be seen.  Aneroid barometer have two pointers One moves independently, the other is stationary, and can be controlled independently due to changes in pressure on the respective box. it is a kind of “forecaster” for the near future. If it is combined with the leading arrow, then within a few minutes you can understand whether the pressure will drop or rise. The index arrow will tilt up or down.

Advantage of aneroid barometer:-

  1. It is compact, portable and can therefore be carried anywhere.
  2. There is no liquid in it and there is no possibility of spreading over the liquid like a mercury barometer.

Disadvantage of aneroid barometer:-

  1. These type of barometer is very less accurate than mercury barometer .
  2. Subject to gradual changes in the sensitivity of the diaphragms, so that they need to be re-calibrated regularly, typically every one to two years.


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