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What is Barometer? Types, Unit and Example

What is barometer?

 A barometer is instrument used to count atmosphere pressure. Also called barometric pressure.

A barometer is a scientific instrument used to measure atmospheric pressure. It helps in forecasting short-term changes in the weather.

 Atmospheric pressure is the force exerted by the weight of air above any given point on the Earth's surface. Barometers can be either mercury-based or aneroid (using a small, flexible metal box).

 Mercury barometers measure pressure by the height of a column of mercury that the atmospheric pressure supports, while aneroid barometers use a small, flexible metal box called an aneroid cell (which expands or contracts with changes in pressure) to measure pressure changes. 

By monitoring changes in atmospheric pressure, meteorologists can make predictions about upcoming weather conditions.

It is already established that there is a simple relation between the height of a column of liquid and the pressure at its base.

 The pressure to be simply visualised in terms of the vertical height, h = p/rg. The height h is

Barometer

termed as pressure head corresponding to pressure p. a free surface would rise, if small tube of sufficient length and open to atmosphere is connected to the pipe fig. 2.

Piezometer tube

Such tube called a piezometer tube, and the height h is the measure of the gauge pressure of the liquid in the pipe. If such piezommeter tube of sufficient length were closed at the top and space above the liquid surface. 

This principle is used in the well-known mercury barometer to calculate local atmospheric pressure. Mercury employed because its density is sufficiently high for a relative short column to be obtained and also because it has very small vapour pressure at normal temperature. 

A perfect vacuum at the top of the tube (Fig.)is never possible; even if no air is present, the space would be occupied by the mercury vapour and the pressure would equal to the vapor pressure of mercury at its existing temperature. 

For accurate work, small corrections are necessary to allow for the variation of r with temperature, the thermal expansion of the scale (usually made of brass), and surface tension effects.

 If water used instead of mercury, corresponding height of column would be about 10.4 m provided that perfect vacuum achieved.

However, the vapour pressure water at ordinary temperature appreciable.ta

The tube smaller in diameter about 15 mm, surface tension effect become significant.

Types of barometers:

Mercury Barometer: It consists of a long glass tube filled with mercury, inverted in a container of mercury. 

Aneroid Barometer: Utilizes a small, flexible metal box (aneroid cell) that expands or contracts with changes in atmospheric pressure. This movement is translated into a measurement displayed on a dial.

Water Barometer: Rarely used, it relies on a column of water instead of mercury. Atmospheric pressure pushes the water up a tube, and the height of the water column indicates the pressure.

Barograph: A barometer that continuously records atmospheric pressure over time. It typically uses an aneroid cell mechanism connected to a pen that records pressure changes on a rotating drum or chart.

Digital Barometer: Modern barometers that use electronic sensors to measure atmospheric pressure and display the readings digitally. They often provide additional features such as temperature and altitude measurements.

Example of Barometer

Barometer consists of a glass tube filled with mercury, inverted in a container of mercury. 

Atmospheric pressure pushes down on the mercury in the dish, causing the mercury column in the tube to rise or fall, indicating changes in pressure. This simple yet effective device has been used for centuries to predict weather changes and is still employed in various forms today.

So in this article we discussed topic Barometer hope you understand well.

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