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Different Types of Barometers

A barometer is a device for measuring the atmospheric pressure. There are different types of barometers. Some of them are described below:

 

Simple Mercury Barometer

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Atmospheric pressure can be measured using a simple mercury barometer. A simple mercury barometer can be made with a clear, dry, thick-walled glass tube about 1 metre ling. The glass tube is sealed at one end and is filled with mercury completely. While filling the tube with mercury care has to be taken so that there are no air bubbles present in the mercury column. Close the open end with thumb and turn the tube upside down carefully over a trough containing mercury. Dip the open end under the mercury level in the trough and remove the thumb.

The mercury level in the tube falls until it is about 76 cm (760 mm) vertically above the mercury level. It is the atmospheric pressure acting on the surface of the mercury in the trough that supports the vertical mercury column.

The atmospheric pressure is therefore specified by so many millimetres of mercury. For example, the atmospheric pressure is 760 mm Hg at sea level (equivalent to 105 Pa).

Testing for vacuum in a barometer

Testing vacuum in a barometer

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Greater the atmospheric pressure, greater is the vertical height of the mercury column. The space above mercury is a vacuum. This empty space is called 'Torricellian vacuum'. This can be shown by tilting the tube till the mercury fills the tube completely.

The Fortin Barometer

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It is an improved version of the simple mercury barometer. It gives more accurate reading of the atmospheric pressure because a vernier scale is used here.

Fortin Barometer

Fortin barometer

The Aneroid Barometer

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It is a type of barometer that does not make use of a liquid. It is commonly used as an altimeter in aircrafts (since the pressure decreases as the height increases) and also for weather forecasts.

Generally, a low pressure or a sudden fall in pressure indicates unsettled weather while a high pressure or a rising pressure is associated with fine weather.

As the atmospheric pressure changes, the top of the metal box moves up and down. Levers magnify this movement and move a pointer over a circular dial.

Aneroid barometer

Aneroid barometer

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