Air Class 7 Social Science Solutions
Study materials for the chapter Air Class 7 Social Science provided here include Questions and Answers, Notes and Videos. Studying this chapter will help the students build a clear concept of the various atmosphere compositions.
Chapter Name: Air
Subject: Social Science
Lesson: 3
Class: 7
Board: Board Of Secondary Education Manipur (BOSEM/BSEM)
Contents: Questions and Answers, Explanation Video and notes
Table of Contents
Questions and Answers for the Chapter Air Class 7 Social Science
You can Access all the solved questions and answers for the chapter Air below
Answer the following questions in a word
1. The lowest layer of the atmosphere
Troposphere
2. The layer which sends back radio signals to the earth
Ionosphere
3. The incoming solar radiation received by the earth.
Insolation.
Answer the following questions in about 30 words each
Q1. Mention the uses of the two most plentiful gases of the atmosphere.
Ans: Nitrogen is vital for life and it consists of 78% of the total volume of the atmosphere.
Oxygen, about 21% of the total volume, is used by humans, animals and other living organisms to breathe.
Q2. Give the significance of the ozone layer to human beings.
Ans: The ozone layer absorbs ultraviolet rays from the sun which is harmful to all living organisms.
Q3. How is the atmosphere heated?
Ans: The heat that falls on the ground surface is transferred to the atmosphere through radiation, conduction, convection, and advection.
Q4. Name the main pressure belts on the surface of the earth.
Ans: Equatorial low-pressure belt.
Subtropical high-pressure belt
Subpolar low-pressure belts
Polar high-pressure belts
Choose the correct answer
I. The process of conversion of water vapour into water droplets is known as
a) Evaporation
b) Condensation
c) Sublimation
d) Precipitation
Ans: Condensation
ii. The condition of the atmosphere at a particular place
a) Weather
b) Climate
c) Pressure
d) Temperature
Ans: Weather
iii. Based on latitude location, Manipur belongs to
a) Tropical zone
b) Torrid zone
c) Temperate zone
d) Frigid zone
Ans: Temperate zone
Mark true or false against the following statements
a) The troposphere is the boundary between the stratosphere and the mesosphere (False)
b) Air pressure is measured by an instrument called a thermometer. (False)
c) Plants absorb carbon dioxide to make food. (True)
d) Water vapour is present in the lower atmosphere. (False)
e) The torrid zone is the hottest part of the earth. (True)
Watch this video: Air Class 7 social Science
BOSEM Notes for Class 7 Social Science Chapter 3 Air
Composition of the atmosphere
The atmosphere is composed of several gases, water vapour, and dust particles.
Nitrogen is the most plentiful gas and occupies 78% of the total volume. Nitrogen is vital for plant life. Oxygen makes up about 21% of the air by volume. Human beings and animals need oxygen to breathe. Green plants produce oxygen. The remaining 1% is made up of gases like carbon dioxide, argon, helium, methane, hydrogen, and ozone.
Dust particles such as smoke, fine dust, salt particles, and ash are also present in the atmosphere. Water vapour is another component in the air and plays an important role in climate.
Based on temperature changes, the atmosphere is divided into 5 layers:
- Troposphere: The lowest layer of the atmosphere. All kinds of weather phenomena occur in this layer due to the presence of dust particles and water vapour. This layer extends for about 12 km on average.
- Stratosphere: Lies above the troposphere. It is a cold and clean layer. The zone of separation between the troposphere and the stratosphere is called the tropopause.
- Mesosphere: Exists above the stratosphere. Ozone is found in the upper stratosphere and mesosphere. The ozone layer absorbs ultraviolet rays from the sun, which is dangerous for our life.
- Thermosphere: Above the mesosphere where the air is very thin. The upper part of the mesosphere and a large part of the thermosphere is called the ionosphere where molecules of gases are ions. The ionosphere reflects radio waves to the earth’s surface.
- Exosphere: The outermost layer of the atmosphere. It has very thin air. Hydrogen and helium gases predominate in this layer.
Elements of weather and climate
The condition of the atmosphere at a particular time and place is called weather. It is assessed in terms of temperature, pressure, humidity, wind, rainfall, etc.
Climate is the average weather condition for a given region over a long period.
Atmospheric Temperature
The degree of hotness and coldness of the air is known as temperature. The amount of solar radiation received by the earth is called insolation.
Based on heat, the surface of the earth is divided into three heat zones:
- Torrid Zone: Lies between the Tropic of Cancer and the Tropic of Capricorn. The sun’s rays are almost vertical throughout the year.
- Temperate Zone: Lies between the Tropic of Cancer and the Arctic Circle in the northern hemisphere and between the Tropic of Capricorn and the Antarctic Circle in the southern hemisphere. Receives less amount of heat.
- Frigid Zone: Lies to the Arctic Circle in the northern hemisphere and to the south of the Antarctic Circle in the southern hemisphere. Here the sun’s rays are very slanting and are the coldest parts of the surface of the earth.
Heating and cooling of the atmosphere
The atmosphere absorbs very little of the solar radiation. From the ground surface, the heat is transferred to the atmosphere through the process of radiation, conduction, convection, and advection.
Factors controlling temperature
The temperature is measured by an instrument called a thermometer. The atmospheric temperature does not remain the same everywhere and varies from place to place. It depends upon a number of factors like latitude, altitude, distances from the sea, prevailing winds, ocean currents, and the slope of the land. The temperature of the air also decreases with height. The Fahrenheit and Celsius scales are used to measure temperature.
Atmospheric pressure
The weight of the air is called atmospheric pressure. Air pressure is measured by an instrument called a barometer. Normal air pressure at sea level is about 76 cm.
Atmospheric pressure decreases with height. The air becomes thinner and thinner as we go up, and its pressure also goes on decreasing.
The main pressure belts on the earth’s surface are the Equatorial Low-Pressure Belt, Sub-Tropical High-Pressure Belts, Sub-Polar Low-Pressure Belts, and Polar High-Pressure Belts.
Wind System
The horizontal movement of air is called wind. The winds which blow throughout the year in a particular direction are called permanent or planetary winds e.g., the Trade Winds, the Westerlies, and the Polar Winds. The winds which blow over a particular season are called periodic winds. The monsoon is an example. Indian agriculture depends very much on the monsoon. ‘Loo’ of the upper Ganga plains and ‘Ashit Awan’ of Manipur are local winds.
Cyclone
A cyclone is an area of low atmospheric pressure in the centre surrounded by high-pressure areas on all sides. Cyclones are devastating to low-lying coastal areas.
Humidity
The water vapour present in the air is known as humidity. Due to the heat of the sun, water evaporates from the water bodies and enters the atmosphere. As the hot air rises, it reaches higher levels of the atmosphere where the temperature is much lower. Due to a decrease in temperature, the water vapour starts converting into water droplets and ice crystals. This process is called condensation.
Rainfall is very important for the survival of plants and animals. Rainfall is of three types: viz, convectional rainfall, orographic rainfall, and cyclonic rainfall. It is measured with the help of a rain gauge.
