11. Water in the atmosphere

 NCERT Questions

1. Multiple choice questions

(i) Which one of the following is the most important constituent of atmosphere for human beings?

a) Water vapour

b) Hydrogen

c) Dust particle

d) Oxygen

Ans.  a) Water vapour

(ii) Which one of the following process is responsible for transforming liquid into vapour?

a) Condensation

b) Transpiration

c) Evaporation

d) Precipitation

Ans. c) Evaporation

(iii) The air that contains moisture to its full capacity.

a) Relative humidity

b) Specific humidity

c) Absolute humidity

d) Saturated air

Ans. d) Saturated air

(iv) Which one of the following is the highest cloud in the sky?

a) Cyrus

b) Stratus

c) Nimbus

d) Cumulus

Ans. a) Cyrus

2. Answer the following questions in about 30 words:

(i) Name the 3 types of precipitation.

Ans. There are many forms of precipitation like dew, fog, rainfall, snowfall, hills, stones, etc.

a) Rainfall: The precipitation in the form of water is called rainfall.

b) Snowfall: When the temperature is lower than the zero degree Celsius. Precipitation takes place in the form of fine flakes of snow and is called snowfall.

c) Hailstones: Sometimes drops of rain, after being released by the clouds, become solidified into small, rounded, solid pieces of ice and reach the surface of the Earth are called hailstones.

(ii) Explain relative humidity.

Ans.

a) The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.

b) It is highest over oceans and lowest over continents.

c) With the change of air temperature, the capacity of retain moisture increases or decreases and the relative humidity is also affected.

(iii) Why does the amount of water vapour decreases rapidly with altitudes?

Ans.

a) The quantity of water vapour existing in the air depends upon the rate of evaporation and the temperature of the air which determines its holding capacity of water vapour.

b) Both temperature and evaporation decreases with altitude, and as a result, water vapour also decreases rapidly with altitude.

(iv) How are clouds formed? Classify them?

Ans. Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of water vapour in free air at considerable elevations. As the clouds are formed at some height over the surface of the earth, they take various shapes. According to their height expense, density and transparency or opaqueness clouds are grouped under 4 types:

a) Cyrus

b) Cumulus

c) Stratus

d) Nimbus

3. Answer the following questions in about 150 words:

(i) Discuss the salient feature of the world distribution of precipitation.

Ans. Salient features of the world distribution of precipitation are:

a) Different places on the Earth surface receive different amounts of rainfall in a year and that too in different seasons.

b) In general, as we proceed from the equator towards the poles, rainfall goes on decreasing steadily.

c) The coastal areas of the world receive greater amount of rainfall than the interior of the continents.

d) The rainfall is more over the oceans than on the land mass of the world.

e) Between the latitudes 35˚ and 40˚ north and south of the equator, the rain is heavier on the eastern coast and goes on decreasing towards the west. But between 45˚ to 65˚ north and south of the equator the rainfall is first received on the western margins of the continents and it goes on decreasing towards the east.

f) In some regions, rainfall is distributed evenly throughout the year, such as in the Equatorial belt and in the western parts of cool temperate region.

On the basis of total amount of annual precipitation, major precipitation regimes of the world are identified as:

i) The Equatorial belt, the windward slopes of the mountains along the western coast in the cool temperate zone and the coastal areas of the monsoon land receive heavy rainfall of over 200 centimetres per annum.

ii) Interior continental areas receive moderate rainfall, varying from 100 to 200 cm per annum.

iii) The coastal areas of the continents receive moderate amount of rainfall.

iv) The central parts of the tropical land and the eastern and the interior parts of the temperate lands receive rainfall varying from 50 to 100 cm per annum.

v) Areas lying in the rain shadow zone of the interior of the continents and high latitudes receive very low rainfall, less than 50 cm per annum.

(ii) What are forms of condensation? Describe the process of dew and frost formation.

Ans. The Transformation of water vapour into water is called condensation. Condensation is caused by the loss of heat. When the water vapour or the moisture in the atmosphere takes one of the forms of dew, frost, fog or clouds condensation takes place. Forms of condensation can be classified on the basis of temperature and location:

a) Condensation takes place when the dew point is lower than the freezing point as well as higher than the freezing point.

b) Dew: When the temperature is deposited in the form of water droplets on cooler surfaces of solid objects rather than nuclei in air above the surface. Such as stones, grass blades and plant leaves. It is known as dew.

c) Frost: Forms on cold surfaces when condensation takes place below freezing point, i.e., the dew point is at or below the freezing point.

d) Fog and mist: When the temperature of an air mass containing a large quantity of water vapour falls all of a sudden condensation takes place within itself on fine dust particles. So the fog is a cloud with its space at or very near up to the ground.

e) Smog: When condensation is mixed with fog and smoke, is described as smog.

f) Clouds: Cloud is a mass of minute water droplets or tiny particles of ice formed by condensation of the water vapour in free air at considerable elevations. As the clouds are formed at some height over the surface of the earth they take various shapes.

 Question Bank:

 Multiple choice questions:

1. What do we say to the amount of water vapours present in the atmosphere?

a) Saturation

b) Humidity

c) Dew points

d) Dew

Ans. b) Humidity

2. The temperature at which saturation occurs in a given sample of air is known as what?

a) Saturation

b) Humidity

c) Dew point

d) Dew

Ans.  c) Dew point

3. Conversion of water vapour into water is called:

a) Fog

b) Dew

c) Humidity

d) Condensation

Ans. d) Condensation

4. What do we call to a situation where fog with smoke is found?

a) Fog

b) Smog

c) Dew

d) Humidity

Ans. b) Smog

5. What is the absolute amount of water vapour present in atmosphere called?

a) Absolute humidity

b) Relative humidity

c) condensation

d) Fog

Ans. a) Absolute humidity

6. At what height are cirrus clouds formed?

a) 8000 to 12,000 metres

b) 3000 to 5000 meters

c) 6000 to 9000 metres

d) 4000 to 7000 meters

Ans. a) 8000 to 12,000 metres

7. At what height are cumulus clouds formed?

a) 8000 to 12,000 metres

b) 3000 to 5000 metres

c) 6000 to 9000 meters

d) 4000 to 7000 metres

Ans. d) 4000 to 7000 metres

8. When the saturated air mass comes across the mountain, it is forced to ascend and as it rises it expands. The temperature falls and the moisture is condensed. It is also known as:

a) Relief rain

b) Cyclonic rain

c) Hail stones

d) Rainfall

Ans. a) Relief rain

9. In atmosphere density of water vapour varies to what per cent?

a) 0 to 4%

b) 5 to 10%

c) 7 to 12%

d) 9 to 15%

Ans. a) 0 to 4%

10. The temperature at which the water starts evaporating is referred to as:

a) Dew point

b) Latent heat of vaporization

c) High temperature

d) Condensation

Ans. b) Latent heat of vaporization

11. Interior continental areas receive:

a) Heavy Rainfall

b) Moderate rainfall

c) Low rainfall

d) Cyclonic rainfall

Ans. b) Moderate rainfall

 Very short answer type questions:

1. What is Smog?

Ans. Such a condition when fog is mixed with smoke is described as smog.

2. How is humidity received in atmosphere?

Ans. The moisture in the atmosphere is derived from water bodies through evaporation and transform from plants through transpiration.

3. What is relative humidity?

Ans. The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.

4. What is absolute humidity?

Ans. The actual amount of the water vapour present in the atmosphere is known as the absolute humidity. It is the weight of water vapour per unit volume of air and is expressed in terms of grams per cubic metre.

5. By what process there is a continuous exchange of water between the atmosphere, the oceans and the continents?

Ans. There is a continuous exchange of water between the atmosphere, the oceans and the continents through the process of evaporation, transpiration, condensation and precipitation generally termed as water cycle.

6. How are clouds classified?

Ans.  According to their height, expense, density and transparency or opaqueness clouds are grouped under 4 types: Cirrus, Cumulus Stratus, and Nimbus.

A combination of these 4 basic types can give rise to the following types of clouds:

a) High clouds: Cirrus, Cirrostratus, cirrocumulus

b) Middle clouds: Altostratus and Altocumulus

c) Low clouds: stratocumulus and nimbostratus formed with fronts/cyclones

d) Clouds with extensive vertical development cumulus and cumulonimbus

7. When does condensation take place?

Ans.  The transformation of water vapour into water is called condensation. Condensation is caused by the loss of heat.

8. What are the suitable conditions for making of dew?

Ans.  The ideal condition for dew formation is clear sky, calm air, high relative humidity and cold and long nights. For the formation of dew, it is necessary that the dew point is above the freezing point.

9. What are hail stones?

Ans.  Sometimes drops of rain water after being released by, the clouds become solidified into small, round; solid pieces of ice and reach the surface of the earth are called hail stones.

10. What is rain shadow area?

Ans.  The area situated on the leeward side, which gets less rainfall is known as the rain shadow area.

11. What is precipitation?

Ans.  After the condensation of water vapour, the release of moisture is known as precipitation. This may take place in liquid or solid forms.

12. What is convectional rain?

Ans.  Air, on being heated, becomes light and rises up with convectional currents. As it rises, it expands and loses heat and consequently condensation takes place and cumulus clouds are formed.  With thunder and lightning heavy rainfall takes place, but this does not last for long.

13. What factors influence the process of condensation?

Ans.  Condensation is influenced by the volume of air, temperature, pressure, and humidity. Condensation takes place:

a) When the temperature of the air is reduced to dew point with its volume remaining constant.

b) When both the volume and the temperature are reduced.

c) When moisture is added to the air through evaporation.

Short answer type questions:

1. Name and define 3 important types of rainfall.

Ans.  On the basis of origin, rainfall may be classified into 3 main types.

a) Convectional rain

b) Orographic or relief rain

c) Cyclonic or frontal rain

a) Convectional rain: The air on being heated becomes light and rises up in convection current. As it rises it expands and loses heat and consequently condensation takes place and cumulus clouds are formed. With thunder and lightning heavy rainfall takes place, but this does not last for long. Such rain is common in the summer or in hotter part of the day. It is very common in the Equatorial regions and interior parts of the continents, particularly in the northern hemisphere.

b) Orographic rain: When the saturated air mass comes across a mountain, it is forced to ascend and as it rises, it expands. The temperature falls and the moisture is condensed. In this sort of rain, the windward slopes receive greater rainfall. After giving rain on the windward side, when these winds reach the other slope they descend and their temperature rises. Their capacity to take in moisture increases and hence these leeward slopes remain rainless and dry. The area situated on the leeward side, which gets less rainfall, is known as the rain shadow area. It is also known as the relief rain.

c) Cyclonic rainfall: These rains take place in low pressure areas where air moves from high pressure area to low pressure area in a circular motion. This movement brings rainfall.

2. Explain the process of evaporation.

Ans.  Evaporation is a process by which water is transformed from liquid to gaseous state. Heat is the main cause for evaporation. The temperature at which the water starts evaporating is referred to as the latent heat of vaporization. Increase in temperature increases water absorption and retention capacity of the given parcel of air. Similarly, if the moisture content is low, air has a potentiality of absorbing and retaining moisture. Movement of air replaces the saturated layer with the unsaturated layer. Hence, the greater the movement of air, the greater is the evaporation.

3. Explain cyclonic rain.

Ans.  Air expands when heated and gets compressed when cooled. This results in variation in the atmospheric pressure. The result is that it causes the movement of air from high pressure to low pressure, setting the air in motion. Air in horizontal motion is built. Atmospheric pressure also determines when the air will rise or sink. The wind redistributes the heat and moisture across the planet thereby maintaining a constant temperature for the planet as a whole. The vertical rising of moist air cools it down to form the clouds and bring precipitation. It is called cyclonic rain.

4. Differentiate between:

 Precipitation and condensation:

Ans.  

Absolute humidity and Relative humidity:

Ans.  

Convection rain and Relief rain:

Ans.  

Fog and Mist:

Ans.  

Long answer type questions

1. Explain condensation in detail.

Ans.  The transformation of water vapour into water is called condensation

a) Condensation: is caused by the loss of heat.

b) Sublimation: When moist air is cold, it may reach a level when its capacity to hold water vapour ceases. Then the excess water vapour condenses into liquid form. If it directly condenses into solid form, it is known as sublimation.

c) Process: In free air, condensation results from cooling around very small particles turned as hygroscopic condensation nuclei. Particles of dust, smoke and salt from the ocean are particularly good nuclei because they absorb water. Condensation also takes place when the moist air comes in contact with some colder object, and it may also take place when the temperature is close to the dew point. Condensation therefore depends upon the amount of cooling and the relative humidity of the air.

Factors affecting condensation:

• When the temperature of the air is reduced to dew point with its volume remaining constant.
• When both the volume and the temperature are reduced.
• When moisture is added to the air through evaporation.

However, the most favourable condition for condensation is the decrease in air temperature. After condensation, the water vapour or the moisture in the atmosphere takes form of dew, frost, fog and clouds.

2. Explain about fog and mist.

Ans.  When the temperature of an air mass containing a large quantity of air vapour falls all of a sudden condensation takes place within itself on fine dust particles. So the fog is a cloud with its base at or very near to the ground.

a) In both the fog and mist, the visibility becomes poor to zero in urban and industrial centres. Smoke provides plenty of nuclei which help in the formation of fog and mist.

b) Such a condition, when fog is mixed with the smoke, is described as smog.

c) The only difference between fog and mist is mist contains more moisture.

d) In mist each nuclei contains a thicker layer of moisture. Mist is frequent over mountains as the warm air rises up the slopes and meets cold surface.

e) Fog is dryer than mist and it is prevalent where warm currents of air come in contact with cold currents. Fog is mini cloud in which condensation takes place around nuclei provided by the dust, smoke and the salt particles.

 HOTS (High Order Thinking Skills)

1. On the basis of rainfall received in how many groups can we classify the world?

Ans.   On the basis of rainfall received, we can classify the world into 5 groups:

a) The Equatorial belt with windward slopes of the mountains along the western coast in the cool temperate zone. And the coastal areas of the monsoon land receive heavy rainfall of over 200 centimetres per annum.

b) Interior continental areas receive moderate rainfall, varying from 100 to 200 cm per annum.

c) The coastal areas of the continents receive moderate amount of rainfall.

d) The central parts of the tropical land and the eastern and the interior parts of the temperate lands receive rainfall varying 50 to 100 cm per annum.

e) Areas lying in the rain shadow zone of the interior of the continents and high latitudes receive very low rainfall, less than 50 cm per annum.

2. Use a diagram to explain the process of evaporation.

Ans.  Evaporation is a process by which water is transformed from liquid to gaseous state, which is the main cause of evaporation. Movement of air replaces the saturated layer with the unsaturated layer. Hence the greater the movement of the air, the greater is the evaporation.