A barometer can be defined as a device that is used to measure atmospheric pressure. We all know that atmospheric pressure changes with altitudes below and above sea level. During the investigation made in Italy in the 17th century, it was known that the mercury barometer was used to find why it was not possible to design a suction pump to lift the water higher than 10 m. Evangelista Torricelli designed the first apparatus which is generally accepted as the first barometer in 1644. By 1648, the barometer was used to serve three purposes: equipment for trailing the laws of physics, a tool to calculate the altitude, and a weather monitor.
A barometer is an instrument that helps in determining the atmospheric pressure and hence helps in weather forecasting and altitude determination. The layer of air enfolded around the earth is known as the atmosphere. This air has weight and presses against everything it touches due to the gravity of the earth. The barometer is used to measure this pressure. Due to changes in the atmospheric pressure, the weather is also affected. Meteorologists use barometers for weather prediction.
Torricellian and aneroid are transitional barometers. Nowadays barometers are electronic, completely having an LCD that shows the pressure readings. The one barometer which is the simplest barometer has a tall closed tube that is standing upside down in the mercury bath. The density of Mercury is greater than water so air pressure lifts the volume of mercury. If we use water in place of mercury then we have required a tall tube which is not suitable for us.
A glass tube was filled with mercury and it was sealed at one end. This was invented and its open end was placed on a dash of mercury. The level always settled at a height of approximately thirty inches. It was concluded that the column of mercury was sustained by the pressure of air on the open surface of mercury.
There are mainly two types of the barometer.
Mercury Barometer
Aneroid Barometer
Mercury barometer is the most popular, simple, basic barometer which uses mercury. At room temperature, the density of Mercury liquid is higher. It is used in this type of barometer because it is convenient to use in comparison to water. Water is less dense so if we want to use water then we have to need a talk tube because air pressure lift will lift the volume of water higher up in the tube in comparison to mercury.
A Mercury barometer has a long glass column or tube containing mercury in it and has markings inched on it. One end of the tube that is the top end is sealed and another bottom end is open in the mercury bowl. During this please be careful that you do not let the air go in the tube. A vacuum is created above the mercury column.
When the mercury rises in the tube, it shows that air pressure is high.
When the mercury falls in the tube, it means that the pressure is low
So, this rise and fall in mercury give the estimation of air pressure which is known as atmospheric pressure.
Hannes Grobe 19:02, 3 September 2006 (UTC), Barometer mercury column hg, CC BY-SA 2.5
Mercury barometers were more accurate but since mercury is poisonous that's why most people use aneroid barometers nowadays. An aneroid barometer consists of a sealed, airtight metal box with the rise or falls in air pressure, this box either presses inside or expands outside. A spring is linked with the box which is in turn connected to an indicator on the dial. This dial is fine-tuned and we can look at the air pressure immediately. This box is made up of an alloy of beryllium and copper.
Apparatus required for making a simple mercury barometer
Barometer tube
Mercury bottle
Clamp
Metre rule
The barometer tube should be filled with mercury until it is nearly full and close the open end with your finger.
Holding the finger on the top invert the tube into the trough full of mercury. Remove the finger. The height of the mercury will fall. Clamp the barometer and measure the height of the mercury column.
Calculate the pressure based on the formula
$$\mathrm{atmospheric\:pressure\:=\:pgh}$$
Here,
ρ=the density of mercury
g= gravitational acceleration
h=height of the mercury column
A barometer is a gadget used for measuring air pressure and altitude. There are various types of barometers i.e., mercury, aneroid, Fortin, and digital barometer. The aneroid barometer is also known as the non-liquid barometer, so it is widely used in different instruments and altimeters. Nowadays the digital barometer is most commonly used. Among these, all barometers Fortin barometers are more accurate.
Q1. Write down the limitations of a simple barometer?
Ans. Some listed drawbacks of barometer are below
The glass tube used in the barometer has no protection.
There are chances to mix impurities because the container is one-sidedly open.
There is no convenience to move the barometer from one place to another place.
Q2. Write down the main factors which affect the barometer most?
Ans. There are mainly three factors that affect the reading of barometers.
Altitude and elevation
Moisture
Temperature of air
Q3. Who invented the pressure measuring device barometer?
Ans. Evangelista Torricelli was known for investigating the barometer. He was an Italian physicist and mathematician also.
Q4. Write down five applications of the barometer?
Ans. There are many applications of the barometer some are listed below
It is used in fluid mechanics
To measure the atmospheric pressure
Weather forecasting and weather analysis
With help of this we can also find the altitude of a place.
In aircraft barometers are used to determine the pressure.
Q5. What is the definition of 1 atm?
Ans. The atmosphere pushes down the mercury and makes it rise to a level of height of 30 inches or 760 mm approximately of the tube at sea level then this air pressure is called one atmosphere or 1 atm.
Q6. Write down the SI unit of pressure.
Ans: Pressure = force per unit area
$$\mathrm{Unit\:of\:Pressure\:=\:Nm^{-2}\:=\:Pascal}$$
Q7. What are the differences between a barometer and a manometer?
Ans. With the help of a barometer, we can only measure the air pressure but with the help of a manometer we can measure the pressure which is less than the atmospheric pressure.
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