Humidity

Answer the following questions

Question 1

What is evaporation? Name the factors that affect evaporation.

Answer

The process of conversion of water into its gaseous state is called evaporation. It may also be termed as vaporization.

The factors affecting evaporation are:

1. Air Pressure — The rate of evaporation is higher when pressure is low.
2. Availability of water — The rate of evaporation is higher where large water bodies are present.
3. Temperature — Evaporation is directly proportional to temperature. The warmer the evaporating surface, the higher the rate of evaporation.
4. Relative humidity — The rate of evaporation in dry air is more than in moist air.
5. Area of evaporating surface — Larger area of evaporating surface offers more evaporation.

Question 2

What is condensation? When does condensation occur?

Answer

A process of change of matter in the gaseous state (water vapour) to the liquid state (water) or solid water state (ice) is known as condensation.

Condensation occurs when:

1. Air is cooled below its dew point.
2. The dew point temperature falls below the freezing point.

Question 3

How does air gets cooled?

Answer

As the warm air rises up, the air pressure drops and the gases expand. The temperature is lower at higher altitudes which results in cooling of the air as well.

Question 4

Name the different forms of condensation.

Answer

The different forms of condensation are:

1. Clouds
2. Dew
3. Frost
4. Fog
5. Mist

Question 5

What is precipitation?

Answer

Precipitation is defined as water in liquid or solid forms falling to the Earth. It can be termed as deposition of atmospheric moisture and is the most important phase of the hydrological cycle. Precipitation cam be in the form of hail, snow, sleet,rain etc.

Question 6

State the conditions necessary for precipitation.

Answer

Following are the conditions necessary for precipitation:

1. The air must be saturated.
2. The temperature at which condensation takes place must be present.
3. The air must contain small particles of matter such as dust around which droplets form.
4. The air must be cooled below its dew point.

Question 7

What are the different forms of precipitation?

Answer

The different forms of precipitation are:

1. Rain
2. Snow
3. Hail
4. Sleet
5. Drizzle
6. Fog
7. Frost

Question 8

How is the convectional rainfall caused?

Answer

The two factors necessary to cause convectional rainfall are intense heating of the surface and abundant supply of moisture. Due to intense heating of the surface, the surface air gets heated and expands and rises up conventionally holding moisture. It is thereby cooled adiabatically and its temperature falls below the dew point, forming Cumulonimbus cloud, which gives heavy rains. Such rainfall is called convectional rainfall.

Question 9

Give two characteristic features of the convectional rainfall. Name an area which commonly experiences this type of rainfall.

Answer

Two characteristic features of the convectional rainfall are:

1. This type of rain mostly occurs at 4 o'clock in the afternoon.
2. It is always torrential accompanied by lightening and thunder.

The area which commonly experiences this type of rainfall is equatorial zone as it experiences direct sun rays throughout the year.

Question 10

What are the chief requirements for orographic rainfall to be experienced? Name a region which experiences it.

Answer

The chief requirements to experience orographic rainfall are:

1. moisture laden winds.
2. mountain in the path of the winds.

It is experienced in the western Ghats. Monsoon winds bring rainfall to the windward side of the ghats while the leeward side remains dry.

Question 11

What is the meaning of rain shadow? Give an example.

Answer

The area on the leeward slope of a mountain range, in the shadow of the mountain where precipitation is greatly reduced compared to windward slope is called rain shadow.

The leeward side of the Western Ghats is an example of rain shadow region.

Question 12

What is cyclonic rainfall? Name a region which experiences this type of rainfall.

Answer

Cyclonic rainfall occurs when a mass of warm air (warm front) meets the mass of cold air (cold Front). The warm air is forced up above the cooler air as it is lighter. Condensation takes place and clouds are formed, followed by rains.

Northwest India experiences this type of rainfall in winters.

Question 13

State the principal factors affecting the distribution of rainfall. Which are the wettest regions of the world?

Answer

The principal factors affecting the distribution of rainfall are:

1. Latitude — The latitudinal belt of maximum precipitation is found in the equatorial Zone between 8° N to 8° S along with the seasonal shifting of the Doldrums. The shifting of the Trade Winds causes winter rains in Mediterranean Regions in Europe. Trade Winds blow from North-East to South-West, they shed maximum moisture on the Eastern margins of the continents and western margins are left dry.
2. Continents and oceans — Places which are located away from the sea in the interior receive relatively less precipitation than coastal areas.
3. Mountain Barriers — They play a great role in the world distribution of precipitation by causing orographic rainfall on the windward side while the leeward side remains dry or receives little rainfall.

The latitudinal belt between 8° N to 8° S is the wettest region of the world.

Question 14

Give two examples of the areas that receive less than 25 cm of rainfall.

Answer

Two examples of the areas that receive less than 25 cm of rainfall are:

1. Desert area of Rajasthan
2. Desert of China(Gobi desert).

Question 15

Explain the process of precipitation in brief.

Answer

The formation of clouds by condensation takes place due to adiabatic cooling. For precipitation air must be saturated and temperature below dew point must be reached. The air must contain small particles of matter such as dust around which droplets form. When the cold droplets, ice pellets or ice crystals grow to such a large size as to overcome the normal buoyancy, precipitation occurs.

Question 16

Name the three types of rainfall.

Answer

The three types of rainfall are:

1. Convectional rainfall
2. Orographic rainfall
3. Cyclonic Rainfall

Question 17

Mention two characteristics of orographic rainfall.

Answer

Two characteristics of orographic rainfall are:

1. When the moisture laden wind rises along the windward slope of the mountain the pressure on it decreases, the air expands and cools.
2. On the leeward side, as the dry air descends the mountain slopes, the pressure decreases.

Question 18

Name the factors necessary for convectional rainfall.

Answer

The factors necessary for convectional rainfall are:

1. Intense heating of the surface.
2. Abundant supply of moisture

Question 19

Where does cyclonic rainfall occur?

Answer

Cyclonic rainfall is common throughout the Doldrums where the Trade winds meet.

Explain the following terms

Question 1

Absolute Humidity

Answer

Absolute humidity is the actual amount of water vapour present in a given volume of air, regardless of temperature. It is expressed as grams of moisture per cubic metre of air (g/m³). The amount of absolute humidity decreases as we go towards the poles. The maximum absolute humidity of warm air at 30°C is approximately 30 gm of water vapour — 30 g/m³.

Question 2

Relative Humidity

Answer

Relative Humidity refers to the water vapour present in the air as compared to the maximum amount of water the air can hold at that temperature. It can be defined as "a ratio between the actual amount of water vapour present in the air and the maximum amount of water the air can hold at that temperature." It is always expressed in percentage.

Question 3

Dew Point

Answer

The temperature at which the air becomes fully saturated with water vapour is known as dew point. It is used to predict dew, frost, fog etc. It can also indicate air's actual water vapour content.

Question 4

Clouds

Answer

Clouds are defined as a visible aggregation of minute water droplets/ice particles in the air above ground level. Clouds can be classified into Low, medium and High, on the basis of their height.

Question 5

Hail

Answer

Hailstones are small round balls of ice with frosted appearance. They are formed of concentric layers of ice much like an onion. Hail stones range from 0.5 to 5 cm in diameter. They occur only from the Cumulonimbus cloud type.

Question 6

Fog

Answer

Condensation of water vapour near the surface of earth leads to formation of fog. Fog is formed when warm and moist air moves along the surface of colder region. It affects visibility. Fog makes it difficult to see the objects beyond 1 km.

Question 7

Snow

Answer

Snow consists of crystals or grains of ice which grow directly from the water vapour. Snow displays beautiful forms of symmetrical patterns that are formed in winter when the temperature is below freezing point.

Question 8

Precipitation

Answer

Precipitation is defined as water in liquid or solid forms falling to the Earth. Hail, snow, sleet, rain and drizzle are the common forms of precipitation.

Distinguish between the following pairs

Question 1

Evaporation and Condensation

Answer

Question 2

Convectional Rainfall and Orographic Rainfall

Answer

Question 3

Dew and Frost

Answer

Give reasons for the following

Question 1

Convectional currents generally lead to rain.

Answer

Convectional currents generally lead to rain as due to intense heating of the surface, the surface air gets heated and expands and rises up conventionally holding moisture. It is thereby cooled adiabatically and its temperature falls below the dew point, forming Cumulonimbus clouds, which give heavy rains.

Question 2

The rain-shadow areas are generally dry.

Answer

The sudden ascent of warm moist air on the windward sides causes cooling of air, leading to condensation and precipitation.
On the contrary, on descending the leeward slope, a decrease in altitude increases both the pressure and the temperature, leading the air to get compressed and warm. Consequently, the relative humidity drops and there is evaporation and little or no precipitation in the rain shadow area. Hence, a rain shadow area is generally dry.

Question 3

Cyclonic rainfall is common in the belt of westerlies.

Answer

Cyclonic rainfall occurs when cold and warm fronts meet. The westerlies blow from the the warmer Horse latitudes towards the poles in north and south hemisphere. This results in the convergence of warm westerlies and cold polar winds, which further results in Cyclonic rainfall. Therefore, Cyclonic rainfall is common in the belt of westerlies.

Question 4

Areas of trade winds are usually dry.

Answer

Areas of trade winds are usually dry because trade winds blow from dry mainland. They lack moisture and hence cannot cause rainfall.

Question 5

Cyclonic rainfall is also known as frontal rainfall.

Answer

Cyclonic rainfall is also known as frontal rainfall because it occurs when warm front (a mass of warm air) meets the cold front (a mass of cold air).

Question 6

Convectional rainfall is also called 4 o'clock shower.

Answer

Convectional rainfall is called 4 o'clock rainfall as this type of rainfall occurs in the afternoon at about 4 o'clock. This is because the heat from the sun builds up throughout the day, causing the air to rise and form clouds that eventually bring rain in late afternoon around 4 o'clock.

Diagrams

Question 1

Draw self-explanatory diagrams to show all the three types of rainfall.

Answer

Below diagram shows Convectional rainfall:

Below diagram shows Orographic rainfall:

Below diagram shows Cyclonic rainfall:

Choose the correct option

Question 1

Which of the following statements related to Relative humidity is not correct?

1. It is a ratio between the actual amount of water vapour present in the air & the maximum amount of water the air can hold at that temperature.
2. Saturated air has 100 percent of relative humidity.
3. Relative humidity increases with more water vapour in the atmosphere.
4. Relative humidity is measured in degrees.

Answer

Relative humidity is measured in degrees.

Question 2

The process through which the water changes from its liquid state into water vapour is called

1. Evaporation
2. Condensation
3. Precipitation
4. Conduction

Answer

Evaporation

Question 3

Which of the following factor controls the condensation?

1. The air temperature must fall below the dew point temperature
2. The relative humidity must be high
3. High rate of cooling
4. All the above

Answer

All the above

Question 4

Identify the type of rainfall seen here.

1. Convectional
2. Orographic
3. Frontal
4. Cyclonic

Answer

Orographic

Question 5

Which of the following regions receive convectional type of rainfall?

1. Temperate zone
2. Equatorial zone
3. Tropical zone
4. Polar areas

Answer

Equatorial zone

Question 6

Which of the following regions receive cyclonic type of rainfall?

1. Temperate zone
2. Mid-latitudinal region
3. Tropical zone
4. All the above

Answer

All the above

Question 7

The principal factors controlling the distribution of precipitation are

1. Latitude
2. Continents & ocean
3. Mountain Barriers
4. All the above

Answer

All the above

Question 8

Which of the following is not a form of condensation?

1. Fog
2. Dew
3. Rain
4. Frost

Answer

Rain

Question 9

The temperature at which air gets saturated is called

1. Melting point
2. Dew point
3. Freezing point
4. Boiling point

Answer

Dew point

Question 10

Which of the following is the component of hydrological cycle?

1. Evaporation
2. Condensation
3. Precipitation
4. All of the above

Answer

All of the above

Question 11

Fog, dew, mist are mainly formed in

1. Summer season
2. Winter season
3. Spring season
4. any

Answer

Winter season

Question 12

Which of the following is a low cloud?

1. Cirrus
2. Cirrostratus
3. Stratus
4. All the above

Answer

Stratus