## Types of barometers, the principle of their action

Barometers can be aneroid and mercury. The word "aneroid" means "basiccally". The principle of operation of such a barometer is quite simple: changes in atmospheric pressure lead to changes in the geometric dimensions of the aneroid, in result, the arrow on the scale moves. These barometers do not contain hazardous elements, therefore, are suitable for use in the home, in terms of Hiking.

In addition to the aneroid, and mercury there are devices for measuring atmospheric pressure used mercury. Under the action of atmospheric pressure changes the height of the mercury column. The indications of the barometers are more accurate, such devices are used at the meteorological stations. Mercury and its vapors are dangerous to humans, so such devices do not use at home.

You can find electronic barometers, as a rule, they are part of home weather stations. Such integrated devices also measure several other quantities (e.g. temperature and humidity) and allow you to fairly accurately predict the weather for the near future. Digital devices are less sensitive to shaking, so it is good to use in cruising.

## The use of barometer

To use the aneroid barometer easy. Need to see what value the arrow is pointing to the device. On the scale of the barometer has zones that are designated as "drought", "clear", "variable", "rain", "storm", as well as the division showing the absolute values. If the pressure is reduced precipitation, if increased, will be clear. As a rule, the barometer has two hands - one moving, it is connected with aneroid capsule, and the second can be rotated. If it is aligned with the arrow indicating the magnitude of the atmospheric pressure, after some time, it is possible to observe in which direction to deviate the movable point.

Normal atmospheric pressure is 760 mm Hg. article when the air temperature is 15 ° C, the so-called sea level. Homemade barometers can measure its value in the range of 700-800 mm Hg. article on not more than 300 m above sea level. Falling pressure indicates deteriorating weather conditions, the approach of rain or snow. Areas with low pressure are called cyclones. Anticyclones are areas with increased pressure, their approach means the arrival of good weather. Barometer set up, if his testimony differs from the testimony the local weather station is more than 8 mm Hg. art For these purposes, provided the adjusting screw located in the rear of the case. When setting up you need to turn it at the angle not more than 45 degrees.

# Advice 2: How to determine atmospheric pressure

Probably almost every day when you watch or listen to the weather reports, you only pay attention to temperature and possible precipitation. But forecasters mention a few important parameters and atmospheric

**pressure**among them. In the General case the atmospheric pressure is the pressure of the atmosphere to the earth's surface and all objects on it. On the human body there is such a pressure, which pressure is equivalent to 15 tons of cargo. But we feel, as our bodies also have air.You will need

- mercury barometer or aneroid barometer. And if you need to continuously take readings of pressure, use a barograph.

Instruction

1

Mercury barometer usually indicates the atmospheric pressure in millimeters of mercury. Just look at the scale of the level of mercury in the flask – and now you know the atmospheric pressure in your room. Typically, this value is 760±20 mm of mercury.St. If you want to know the pressure in Pascal, you use the simple transfer system: 1 mm. Hg.St. = Cash consideration of 133,3 PA. For example, 760 mm of mercury.St. = Cash Consideration Of 133,3*760 PA = 101308 PA. This pressure is considered normal at sea level at 15°C.

2

To remove the pressure readings from the scale of the barograph is also very simple. This device is based on the action of aneroid boxes, which responds to changes in air pressure. If the pressure increases the wall of the box cave in if the pressure is reduced, walls straightened. The whole system is connected with an arrow, and you just have to see what the atmospheric pressure value the arrow is pointing on the scale of the instrument. Don't be alarmed if the scale is in units such as hPa is hectopascal: 1 hPa = 100 PA. And for translation in a more familiar mm of mercury.St. just use the equation from the previous paragraph.

3

And to find the atmospheric pressure at any particular altitude is possible even without the use of the device, if you know the pressure at sea level. You will need some math skills. Use this formula:P=P0 * e^(-Mgh/RT).In this formula:P is the desired pressure at the height h;

P0 is the pressure at sea level in Pascals;

M is the molar mass of air, equal to 0.029 kg/mol;

g – earth's gravitational acceleration, approximately equal to 9.81 m/S2;

R is the universal gas constant, is taken to be 8.31 j/mol K;

T – temperature in Kelvin (to convert from °C to K, use the formula

T = t + 273, where t is the temperature in °C);

h – the height above sea level, where we find the pressure is measured in meters.

P0 is the pressure at sea level in Pascals;

M is the molar mass of air, equal to 0.029 kg/mol;

g – earth's gravitational acceleration, approximately equal to 9.81 m/S2;

R is the universal gas constant, is taken to be 8.31 j/mol K;

T – temperature in Kelvin (to convert from °C to K, use the formula

T = t + 273, where t is the temperature in °C);

h – the height above sea level, where we find the pressure is measured in meters.

Useful advice

As you can see, don't even have to be in a specific location to measure atmospheric pressure. It can be easily calculated. Look at the last formula, the higher we ascend above the earth, so it will be below atmospheric pressure. And already at the height of 4000 metres, water will boil at temperature of 100°C, as we used to, and approximately at 85°C because the pressure there is not 100 of 500 PA, and around 60,000 PA. Therefore, the process of cooking food at this altitude becomes longer.