# IAS Prelims Study Material: Pressure Belt

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Here, we have provided GS Geography questions for IAS Prelims Exam 2019 which will serve as the best practice questions before IAS Prelims Exam.

1. Consider the following statements regarding the atmospheric pressure:

1. The weight of the column of air at a given place and time is called air pressure or atmospheric pressure.
2. Atmospheric pressure is measured by an instrument called Thermometer.
3. Atmospheric pressure is measured as force per unit area and the unit used for measuring pressure is called millibar.

Which of the above statements is/are correct?
a. 2 only
b. 1 and 3
c. 2 and 3
d. 1, 2 and 3

Explanation:

The atmosphere is held on the earth by the gravitational pull of the earth. A column of air exerts weight in terms of pressure on the surface of the earth. The weight of the column of air at a given place and time is called air pressure or atmospheric pressure. Atmospheric pressure is measured by an instrument called barometer. Nowadays, Fortin’s barometer and Aneroid barometer I are commonly used for measuring air pressure.

Atmospheric pressure is measured as force per unit area. The unit used for measuring pressure is called millibar. Its abbreviation is ‘mb’. One millibar is equal to the force of one gram per square centimetre approximately.

Movements of Ice, Wind and Sea Waves

2. Air pressure decreases with:
a. The decrease in altitude
b. Increase in altitude
c. The decrease in density of air
d. Decrease in the temperature of air

Explanation:

The columnar distribution of atmospheric pressure is known as vertical distribution of pressure. Air pressure decreases with increase in altitude but it does not always decrease at the same rate. Dense components of the atmosphere are found in its lowest parts near the mean sea level. The temperature of the air, amount of water vapour present in the air and gravitational pull of the earth determines the air pressure of a given place and at a given time. Since these factors are variable with change in height, there is a variation in the rate of decrease in air pressure with an increase in altitude.

3. Consider the following statements regarding the air temperature and the air pressure on various regions on earth:
1. Air pressure is low in equatorial regions and it is higher in Polar Regions.
2. There is an inverse relationship between air temperature and air pressure.
3. Low air pressure in equatorial regions is due to the fact that hot air ascends there with a gradual decrease in temperature causing thinness of air on the surface.

Which of the above statements is/are correct?
a. 2 only
b. 1 and 3
c. 2 and 3
d. 1, 2 and 3

Explanation:

In the previous lesson, we have studied that the earth is not heated uniformly because of unequal distribution of insolation, differential heating and cooling of land and water surfaces. Generally, there is an inverse relationship between air temperature and air pressure. The higher the air temperature, the lower is the air pressure.

The fundamental rule about gases is that when they are heated, they become less dense and expand in volume and rise. Hence, air pressure is low in equatorial regions and it is higher in polar regions. Along the equator lies a belt of low pressure known as the “equatorial low or doldrums”.

Low air pressure in equatorial regions is due to the fact that hot air ascends there with a gradual decrease in temperature causing thinness of air on the surface. In polar region, cold air is very dense hence it descends and pressure increases. From this we might expect, a gradual increase in average temperature thords equator. However, actual readings taken on the earth’s surface at different places indicate that pressure does not increase latitudinally in a regular fashion from the equator to the poles. Instead, there are regions of high pressure in subtropics and regions of low pressure in the subpolar areas.

Origin and Evolution of Earth

4. Earth’s rotation generates which of the following force?
a. Centrifugal force
b. Centripetal force
c. Kinetic Force
d. Static force

Explanation:

The earth’s rotation generates centrifugal force. This results in the deflection of air from its original place, causing a decrease in pressure. It is believed that the low-pressure belts of the sub-Polar Regions and the high-pressure belts of the sub-tropical regions are created as a result of the earth’s rotation. The earth’s rotation also causes convergence and divergence of moving air. Areas of convergence experience low pressure while those of divergence have high pressure.

5. Consider the following statements regarding the equatorial low-pressure belt:
1. The equatorial low-pressure belt extends from the equator to 100N and 100S latitudes.
2. The equatorial low-pressure belt is called doldrums (the zone of calm) due to excessive heating horizontal movement of air is absent here and only conventional currents are there.

Which of the above statements is/are correct?
a. 2 only
b. 1 and 2
c. 2 and 3
d. 1, 2 and 3