- Composition and structure of atmosphere
NCERT Questions:
- Multiple choice questions:
(i) Which one of the following gases constitutes the major portion of the atmosphere?
a) Oxygen
b) Nitrogen
c) Argon
d) Carbon dioxide
Ans. b) Nitrogen
(ii) Atmospheric layer important for human beings is:
a) Stratosphere
b) Mesosphere
c) Troposphere
d) Ionosphere
Ans. c) Troposphere
(iii) Sea salt, pollen, ash, smoke soon fine soil these are associated with:
a) Gases
b) Dust particles
c) Water vapour
d) Meteors
Ans. b) Dust particles
(iv) Oxygen gas is in negligible quantity at the height of atmosphere:
a) 90 km
b) 120 km
c) 100 km
d) 150 km
Ans. b) 120 km
(v) Which one of the following gases is transparent to incoming solar radiation and opaque to outgoing terrestrial radiation?
a) Oxygen
b) Nitrogen
c) Helium
d) Carbon dioxide
Ans. d) Carbon dioxide
- Answer the following questions in about 30 words:
(i) What do you understand by atmosphere?
Ans.
a) Atmosphere is a mixture of different gases and it envelops the Earth all round.
b) It contains life giving gases like oxygen for humans and animals, and carbon dioxide for plants.
c) The air is an integral part of the Earth mass, and 99% of the total mass of atmosphere is confined to the height of 32 km from the Earth’s surface.
d) The air is colourless and odourless and can be felt only when it blows as wind.
(ii) What are the elements of weather and climate?
Ans. The main elements of weather and climate are subject to change and which influence human life on Earth or temperature, pressure, winds, humidity, clouds and precipitation.
(iii) Describe the composition of atmosphere.
Ans.
a) The atmosphere is composed of gases, water vapour and dust particles.
b) The proportion of gases changes in the higher layers of the atmosphere in such a way that oxygen will be almost in negligible quantity at the height of 120 kilometre.
c) Similarly, carbon dioxide and water vapour are found only up to 90 kilometres from the surface of the Earth.
(iv) Why is troposphere the most important of all the layers of the atmosphere?
Ans.
a) The troposphere is the lowermost layer of the atmosphere. Its average height is 13 kilometre and extends roughly to a height of 8 kilometre near the poles and about 18 kilometre at the equator.
b) Thickness of the troposphere is greatest at the equator because heat is transported to great heights by strong convection currents.
c) This layer contains dust particles and water vapour. All changes in climate and weather take place in this layer.
d) The temperature in this layer decreases at the rate of 1˚C for every 165 metre of height.
e) This is the most important layer for all biological activity.
f) The zone separating the troposphere from stratosphere is known as the tropopause. The air temperature at the tropopause is about 80˚C on the equator and about -45˚C on the poles.
g) The temperature here is nearly constant and hence it is called Tropopause.
- Answer the following questions in about 120 words:
(i) Describe the composition of atmosphere.
Ans.
a) The atmosphere is composed of gases, water vapour and dust particles.
b) The proportion of gases changes in the higher layers of the atmosphere in such a way that oxygen will be almost in negligible quantity at the height of 120 kilometre.
c) Similarly, carbon dioxide and water vapour are found only up to 90 kilometres from the surface of the Earth.
d) Carbon dioxide is meteorologically very important gas, as it is transparent to the incoming solar radiation but opaque to the outgoing terrestrial radiation.
e) It is largely responsible for the greenhouse effect.
f) The volume of other gases is constant, but the volume of carbon dioxide has been rising in the past few decades, mainly because of the burning of fossil fuels. This has also increased the temperature of the air.
g) Ozone is another important component of the atmosphere found between 10 and 50 km above the Earth’s surface and acts as a filter and absorbs the ultraviolet rays radiating from the sun and prevents them from reaching the surface of the Earth.
h) Water vapour is also a variable gas in the atmosphere which decreases with altitude. In the warm and wet tropics, it may account for 4% of the air by volume, while in the dry and cold areas of desert and Polar Regions it may be less than 1% of the air.
i) Water vapour decreases from the equator towards the poles.
j) It also absorbs parts of the insolation from the sun and preserves the Earth’s radiated heat.
k) Dust particles are generally concentrated in the lower layers of the atmosphere. Convectional air currents may transport them to great heights.
l) Atmosphere has a sufficient capacity to keep small solid particles which may originate from different sources and include sea salts, fine soil, smoke, soot, ash, pollen, dust and disintegrated particles of meteors.
m) The higher concentration of dust particles is found in subtropical and temperate regions due to dry winds in comparison to Equatorial and Polar Regions.
n) Dust and salt particles act as hygroscopic nuclei around which water vapour condenses to produce clouds.
Question Bank:
Multiple choice questions:
- Which one of the following is an important component of atmosphere?
a) Water vapours
b) Dust particles
c) Gases
d) All of the above
Ans. d) All of the above
- What is the upper layer of mesosphere called?
a) Mesopause
b) Hydrosphere
c) Troposphere
d) Stratosphere
Ans. a) Mesopause
- Which layer of atmosphere has electrically charged particles?
a) Mesosphere
b) Ionosphere
c) Troposphere
d) Stratosphere
Ans. b) Ionosphere
- Which of the following is the uppermost layer of the atmosphere?
a) Exosphere
b) Ionosphere
c) Troposphere
d) Stratosphere
Ans. a) Exosphere
- Which of the following is the lowest layer of the earth?
a) Mesosphere
b) Ionosphere
c) Troposphere
d) Stratosphere
Ans. c) Troposphere
- The air is an integral part of the Earth’s mass, and 99% of the total mass of the atmosphere is confined to the height of how many kilometres from the Earth’s surface:
a) 10 km
b) 12 km
c) 24 km
d) 32 km
Ans. d) 32 km
- To what height carbon dioxide and water vapour are found in atmosphere?
a) 60 km
b) 75 km
c) 90 km
d) 100 km
Ans. c) 90 km
- To what height is ozone found?
a) 10 to 50 km
b) 5 to 60 km
c) 30 to 80 km
d) 40 to 90 km
Ans. a) 10 to 50 km
- Which of the following layer of atmosphere is most important for life?
a) Nitrogen
b) Oxygen
c) Ozone
d) Carbon dioxide
Ans. c) Ozone
- What are the causes behind increasing density of carbon dioxide?
a) Burning of fossil fuels
b) Killing animals
c) Exploitation of minerals
d) Ozone layer depletion
Ans. a) Burning of fossil fuels
Very short answer type questions:
- By which element is atmosphere made up of?
Ans. Atmosphere is made up of gases, water, vapours and dust particles.
- What percentage of earth mass is constituted by air and it is confined to what height?
Ans. The air is an integral part of the Earth mass, and 99% of the total mass of the atmosphere is confined to the height of 32 km from the Earth surface.
- How does the composition of air keep changing in upper layers of the earth?
Ans. The proportion of gas changes in the higher layers of the atmosphere in such a way that oxygen will be almost in negligible quantity at the height of 120 km. Similarly, carbon dioxide and water vapour are found only up to 90 km from the surface of the Earth.
- Ozone is an important constituent of atmosphere. How?
Ans. Ozone is another important component of atmosphere. It is found between 10 and 50 km above the earth surface and acts as a filter. It absorbs the ultraviolet rays radiating from the sun. It prevents them from reaching the surface of the Earth.
- What do you mean by tropopause?
Ans. The layer separating the troposphere from stratosphere is known as the tropopause.
- What is an important feature of stratosphere?
Ans. The stratosphere is found above the tropopause and extends up to a height of 50 km. One important feature of the stratosphere is that it contains the ozone layer. This layer absorbs ultraviolet radiation and shields life on the Earth from intense, harmful UV rays.
- What is an important feature of troposphere?
Ans.
a) The troposphere is the lower most layer of the atmosphere. Its average height is 13 km and extends roughly to a height of 8 km near the poles and 18 km at the equator.
b) Thickness of the troposphere is greatest on the equator because heat is transported to great heights by strong convectional currents.
c) This layer contains dust particles and water vapour. All changes in climate and weather take place in this layer.
d) The temperature in this layer decreases at the rate of 1˚ C for every 165 metre of height.
- Name the gases found in atmosphere.
Ans. The atmosphere is composed of gases, water vapour and dust particles. Nitrogen constitutes 78.8%. Oxygen contributes 20.94% and Argon contributes 0.93% in atmosphere. Other gases include carbon dioxide, helium, ozone, methane, hydrogen, Krypton, xenon and neon etc.
- Explain important features of ionosphere.
Ans. The ionosphere is located in between 80 to 400 km above the mesopause. It contains electrically charged particles known as ions and hence it is known as ionosphere. Radio waves transmitted from the Earth are reflected back to the Earth by this layer. Temperature here starts increasing with height.
- Write a short note on water vapour.
Ans.
a) The amount of water vapour decreases with the altitudes. In warm and wet tropics it accounts for 4% of the air by volume, whereas in dry and cold areas of deserts and Polar Regions it may be less than 1% of the air.
b) It also decreases from the equator towards the poles.
c) It absorbs parts of the insolation received from the sun and preserves the earth’s radiated heat, and thus acts as a blanket by allowing the earth neither to become too hot nor too cold.
- Explain about the dust particles.
Ans.
a) Dust particles are concentrated in the lower layers of the atmosphere, but sometimes convectional current take them to the higher height.
b) Dust particles include sea salts, fine soil, smoke, ashes and pollen dust and disintegrated particles of meteors.
c) Dust particles and salt particles act as hygroscopic nuclei around which water condenses into water vapour to produce clouds.
d) Dust particles produce optional phenomena. This makes the sky look beautiful at dawn and dusk.
e) Sky looks blue due to the presence of dust particles and water vapour which are scattered in the atmosphere.
- Write about elements of weather and climate in detail.
Ans.
a) The main elements of atmosphere which are subject to change and which influence human life on Earth are temperature, pressure, winds, humidity, clouds and precipitation.
b) These elements act and react on each other.
c) These elements determine the direction and speed of wind, amount of sunlight received, cloud formation and amount of rainfall. These in turn affect weather and climate.
d) These factors behave differently in different places.
e) All these elements are affected by a number of factors in turn. For example, temperature is affected by latitude and height, humidity is affected by distance from the sun, and pressure is affected by height from sea level.
- Write about the structure of atmosphere in detail.
Ans. Structure of atmosphere: The layers of atmosphere differ from one another with respect to density and temperature. On the basis of chemical composition, the atmosphere is mainly divided into.
a) Homosphere
b) Hetrosphere
a) Homosphere
It extends up to 90 km.
It is uniform in chemical composition.
It consists of 3 layers.
i) Troposphere
ii) Stratosphere
iii) Mesosphere
i) Troposphere:
- Lowermost layer of atmosphere.
- Average height is 13 kilometre, although it is roughly 8 km on poles and 18 kilometre on the equator.
- The thickness of troposphere is greater at equator due to upward transportation of heat by convectional current.
- This layer consists of dust particles and water vapour.
- The temperature decreases with height in this layer at a rate of 1˚ C for every 165 metre. This is known as normal lapse rate.
- This layer is important for all biological activities beside that, all climatic and weather conditions take place in this layer.
Tropopause:
- The upper limit of troposphere separating it from stratosphere is called tropopause.
- It is very unstable and a very thin layer of 1.5 kilometre thickness.
- The temperature of tropopause is -80˚ C at equator and -40˚ C at poles.
- The jet plane and other activities occur in this layer.
ii) Stratosphere:
- It extends up to 50 km.
- It is thicker at poles than at equator.
- The temperature is almost constant in its lower portion up to 20 kilometres and then it gradually increases up to 50 km due to the presence of ozone, which absorbs UV rays.
- The temperature rises in the upper limits of the stratosphere as there are no clouds, no convectional currents, no dust particles, and the air moves in the horizontal direction.
- The upper limit of stratosphere is called stratopause.
iii) Mesosphere:
- It extends from 50 to 90 km.
- The temperature decreases with height in this layer and falls up to -100˚C at a height of 80 – 90 km. This is due to noctilucent clouds in higher altitudes.
b) Hetrosphere:
It consists of 2 layers:
i) Ionosphere
ii) Exosphere
i) Ionosphere:
- It extends from 80 to 400 km above the mesopause.
- It contains electrically charged particles known as ions.
ii) Exosphere
- It is the uppermost layer of the atmosphere above the ionosphere.
HOTS
- What would happen if there is no ozone in the atmosphere?
Ans.
a) It is the special variety of layer which is found in a small quantity in atmosphere 10 to 15 km above the Earth’s surface.
b) It acts as a filter and absorbs UV radiation from the Sun and prevents them from reaching the Earth’s surface.
c) If ozone layer is not there, then UV rays will reach the surface of the earth, there will be extreme skin problems, instance of cancer, and in all probabilities life would not have been possible on the earth.
- What is the role of dust particles in atmosphere?
Ans.
a) The atmosphere has sufficient capacity to keep small solid particles which may originate from different sources and includes sea salts, fine soil, smoke, soot, ash, pollen, dust and disintegrated particles of meteors. Dust and solid particles act as hygroscopic nuclei around which water vapour condenses to produce clouds.