Class 7 Geography Chapter 4 Question Answers - Air

Short Answer Type Questions

Q1: Define the term atmosphere.
Ans: The blanket of air surrounding the earth is known as the atmosphere.

Q2: Atmosphere plays a dynamic role how?
Ans: Among the four major elements of the environment, the atmosphere is the most dynamic as changes occur not only from one season to another but also over shorter periods of a few hours.

Q3: What is air circulation?
Ans:  When air is heated it becomes lighter and goes up. Cold air is denser and heavy which is why it tends to sink. When hot air rises, cold air from the surrounding area rushes there to fill the gap. This is how air circulation takes place.

Q4: Name the different layers of the atmosphere.
Ans: The different layers of the atmosphere are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

Q5: What is the greenhouse effect?
Ans: Carbon dioxide in the atmosphere traps the heat radiated from the earth creating a greenhouse effect. This makes the temperatures livable. Without this earth would have been too cold to live. But the increased emissions from vehicles and factories increase the temperature leading to global warming.

Q6: (i) Which layer makes weather phenomena possible? 
        (ii) Which layer has the most suitable conditions for flying aeroplanes?
        (iii) Which layer makes radio communication possible? 
        (iv) Which layer protects us from meteors and obsolete satellites from outer space?
Ans: (i) Troposphere 

(ii) Stratosphere

(iii) Ionosphere

(iv) Thermosphere

Q7: Name the instrument which measures temperature.
Ans: Temperature is measured with the help of a thermometer. Outdoor temperature is measured with the help of a mercury thermometer.

Q8: What do you mean by maximum and minimum temperature?
Ans: Maximum temperature is the highest temperature of the day recorded at about 2.00 pm.

Q9: Define low and high pressure.
Ans: In areas where temperature is high the air gets heated and rises. This creates a low-pressure area. In the area having low temperature the air is cold. It is therefore heavy. Heavy air sinks and creates high pressure.

Q10: Which layer is free from water vapour and dust particles?
Ans: The stratosphere is free from water vapour and dust particles.

Q11: Define wind.
Ans: Moving air is called wind. Wind always blows from high pressure to low pressure.

Q12: What is moisture?
Ans: This term refers to the degree of moisture present in the air. There is a definite limit to the quantity of moisture that can be held by the air at a specific temperature.Moisture

Q13: What do you mean by absolute humidity?
Ans: The total amount of water vapour that is contained in the air at a given temperature is known as absolute humidity.

Q14: Define the term relative humidity.
Ans:  The ratio between the actual amount of water vapour present in the air at a given temperature and the maximum amount of water vapour that the atmosphere can retain at that temperature is known as relative humidity.

Q15: What is rain? What is the importance of rainfall?
Ans: Precipitation in liquid form is called rain. Rainfall is very important for the survival of plants and animals. It brings fresh water to the earth’s surface. If rainfall is less it may cause drought on the other hand if it is more floods will take place.

Long Answer Type Questions

Q1: Describe the composition of the atmosphere.
Ans: The atmosphere consists of a mixture of gases having a relatively uniform composition in the lower layer. An average sample of pure dry air consists of nitrogen (78 %), oxygen (21%) and argon (0.9 %), other gases such as carbon dioxide, hydrogen helium and ozone are present in minute quantities. The lower layer of the atmosphere also contains water vapour in variable quantities.Composition of atmosphere

Q2: What is global warming? What is its effect?
Ans: When the heat retained through greenhouse gases increases the temperature of the earth, it causes global warming:

• The plants maintain the balance of gases. This balance is upset by burning fuels such as coal, petroleum oil and large-scale deforestation.
• This rise in temperature causes the snow in the coldest parts to melt.
• As a result, the sea level rises causing floods in the coastal areas. This may bring changes in weather and climate leading to the extinction of certain plants and animal species.

Q3: Explain how the oxygen and carbon dioxide balance is maintained in the air.
Ans: Green plants use carbon dioxide to make their food and during this process release oxygen:

1. Humans and animals release carbon dioxide and take oxygen from the air.
2. The amount of carbon dioxide released by them is equal to the amount used by plants to make their food. 
3. But now the excess of carbon dioxide is released by burning of fuels. The reduction in several plants upset the balance of gases like carbon dioxide affecting the earth’s weather and climate.

Q4: What is the difference between weather and climate?
Ans: Differences between weather and climate are as follows:

1. Climate 
   • Climate is the atmospheric condition of a particular location over a long-term period. The atmospheric elements of a place are considered the climate of that particular region.
   • These atmospheric elements include temperature, solar radiation, precipitation, humidity, wind, and atmospheric pressure. 
   • Depending on these elements and their variants, respective centres of a specific zone maintain climate records.
2. Weather 
   • Weather is the daily atmospheric conditions of a specific place. 
   • The atmospheric conditions like the brightness of the sun, wind, visibility, humidity, cloudiness, temperature, etc. measure the weather of a particular day and time. 
   • Weather can change within minutes, hours, or even as per season. These changes mostly happen in the closest atmospheric layer to the ground called the troposphere. Nowadays, due to satellite observation, weather prediction has become easy.

Q5: What is global warming? What is its effect? 
Ans: When the heat retained through greenhouse gases increases the temperature of the earth, it causes global warming: 

1. The plants maintain the balance of gases. However, this balance is upset by burning fuels such as coal, petroleum oil and large-scale deforestation.
2. This rise in temperature causes the snow in the coldest parts to melt.
3. As a result, the sea level rises causing floods in the coastal areas.
4. This may bring changes in weather and climate leading to the extinction of certain plants and animal species.

Q6: What is the relation between temperature and pressure?
Ans: The distribution of air pressure is influenced by the temperature of the area:

1. Where temperature is high the air gets heated and rises. This creates a low-pressure area.
2. Low pressure is associated with cloudy skies and wet weather.
3. In areas with low temperatures, the air is cold and heavy so, it sinks down. This creates a high-pressure area.
4. High pressure is associated with clear and sunny skies.
5. Air always moves from high-pressure to low-pressure areas.

Q7: What are the various categories of wind? Explain with a diagram.
Ans: Winds can be broadly divided into three types:

1. Permanent winds – which blow constantly throughout the year in a particular direction.
   Example, easterlies and westerlies.
2. Seasonal winds – which change directions in different seasons. For example, monsoon winds.
3. Local winds – blow only during a particular period of the day or the year in a small area. For example, land or sea breeze, or loo.