Humidity

Choose the correct option

Question 1

The process by which water vapour enters the atmosphere on heating:

1. Water Vapour
2. Evaporation
3. Humidity
4. Precipitation

Answer

Evaporation

Question 2

The process by which water vapour forms water droplets on cooling:

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

Answer

Condensation

Question 3

The process by which water falls to the ground in liquid, solid and frozen form :

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

Answer

Precipitation

Question 4

The amount of water vapour present in air:

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

Answer

Humidity

Question 5

The heat that passes into water vapour in a hidden form:

1. Condensed heat
2. Humidity
3. Latent heat
4. Relative Humidity

Answer

Latent heat

Question 6

Which amongst the following is NOT one of the factors favouring evaporation?

1. Humidity
2. Supply of heat
3. Winds
4. Precipitation

Answer

Precipitation

Question 7

The ratio between the absolute humidity of a given mass of air and the maximum amount of water vapour that it can hold at the same temperature:

1. Humidity
2. Dew Point
3. Relative humidity
4. Latent heat

Answer

Relative humidity

Question 8

The temperature at which air gets fully saturated:

1. Humidity
2. Dew Point
3. Relative humidity
4. Latent heat

Answer

Dew Point

Question 9

The measure of the actual amount of water vapour in the air, regardless of temperature:

1. Absolute Humidity
2. Humidity
3. Dew Point
4. Relative Humidity

Answer

Absolute Humidity

Question 10

The process by which products of condensation, viz water droplets, ice crystals, sleet etc. fall to the ground:

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

Answer

Precipitation

Question 11

Which of the following is not a type of a cloud:

1. Cirrus
2. Cumulus
3. Strata
4. Stratus

Answer

Strata

Question 12

Which of the following type of cloud has a cauliflower-like shape?

1. Cirrus
2. Cumulus
3. Strata
4. None of the above

Answer

Cumulus

Question 13

Condensation nuclei are :

1. impurities that support condensation.
2. water particles that help in precipitation.
3. droplets formed as a result of condensation.
4. droplets that fall to the ground.

Answer

impurities that support condensation

Question 14

Which of the following is NOT correct ?

1. Frontal rainfall: cyclones
2. Convectional rainfall: 4 o'clock showers
3. Cyclonic rainfall: mountains
4. Relief rainfall : mountain barriers

Answer

Cyclonic rainfall: mountains

Short Answer Questions

Question 1

What determines the amount of water vapour in the air?

Answer

The amount of water vapour in the air is determined by temperature. The hotter the air, the more the water vapour present in it. When the atmospheric temperature is low, water vapour is less.

Question 2

How is relative humidity determined?

Answer

Relative humidity is expressed as the ratio between the absolute humidity of a given mass of air and the maximum amount of water vapour that it can hold at the same temperature.

Question 3

Name four chief forms of condensation.

Answer

Four chief forms of condensation are-

1. Clouds
2. Dew
3. Frost
4. Fog and mist

Question 4

Mention the different forms of precipitation.

Answer

The different forms of precipitation are-

1. Rain
2. Snow
3. Hail

Question 5

Give one difference between fog and mist.

Answer

Question 6

What do you understand by 'condensation nuclei'?

Answer

Condensation occurs only around tiny solid particles like dust or carbon dioxide in smoke. These impurities in air are known as condensation nuclei.

Question 7

State the three types of rainfall.

Answer

The three types of rainfall are-

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

Question 8

Why is orographic rainfall also called relief rainfall?

Answer

Orographic rainfall is caused by the relief of the land as it occurs from the cooling of warm moist air which ascends above the mountain barrier lying in the direction of the prevailing winds. The presence of mountains causes humid air to rise. The sudden ascent causes cooling of air, leading to condensation and precipitation. Hence, it is also called relief rainfall.

Question 9

What is cyclonic rainfall? What are fronts?

Answer

Cyclonic rainfall occurs due to cyclones and depressions irrespective of relief or convection. It is caused by convergence of two different air masses with different temperatures and other physical properties. When warm and cold air masses confront each other, the warmer air generally climbs above the colder air. The boundary zones of these air masses are called the fronts.

The rising air is cooled while undergoing a frontal lift. This causes precipitation. Such precipitation is called cyclonic rainfall.

Explain the following terms

Question 1

Precipitation

Answer

The process by which the droplets fall to ground in liquid, solid or frozen form is known as precipitation.

Question 2

Evaporation

Answer

The process by which water vapour enters the atmosphere on heating is known as evaporation.

Question 3

Condensation

Answer

The process by which water vapour forms water droplets on cooling is known as condensation.

Question 4

Humidity

Answer

The amount of water vapour present in air is known as humidity.

Structured Questions

Question 1(a)

What is 'humidity'? How is humidity measured?

Answer

The amount of water vapour present in air is known as humidity.

Humidity of the atmosphere is measured with the help of a hygrometer.

Question 1(b)

Distinguish between Absolute Humidity and Relative Humidity.

Answer

Question 1(c)

Give a geographical reason for each of the following:

(i) The total volume of water in the oceans and seas remains constant.

(ii) In Equatorial regions the sky often remains overcast with clouds.

(iii) Human comfort depends on humidity.

Answer

(i) The total volume of water in the oceans and seas remains constant because all the water that evaporates from the earth's water bodies is eventually returned to it directly by the process of condensation and precipitation, and indirectly by stream and overflow from land surfaces.

(ii) In Equatorial regions the sky often remains overcast with clouds due to excessive heat. The high temperature leads to the rapid heating of air. Such heated air rises in convectional currents, leading to development of clouds at about 10 km height.

(iii) Human comfort depends on humidity because highly humid air is more oppressive. The human body dissipates heat through perspiration and its evaporation. Under conditions of high relative humidity, the rate of evaporation of sweat from the skin decreases and the human being feels warm and uncomfortable.

Question 1(d)

Draw a well labelled diagram showing orographic rainfall.

Answer

Below labelled diagram shows orographic rainfall:

Question 2(a)

What is condensation? Explain briefly the process of condensation.

Answer

The process by which water vapour forms water droplets on cooling is known as condensation.

During condensation, the latent heat locked in water vapour is released back into the atmosphere. Condensation can take place only when water vapour is added to saturated air or when the temperature falls below the temperature at which air becomes saturated.

Question 2(b)

Explain the atmospheric conditions that favour condensation.

Answer

The atmospheric conditions that favour condensation are-

1. There should be a high amount of water vapour present in atmosphere.
2. Minuscule particles of dust, salt and even smoke act as condensation nuclei.
3. The temperature of air must be below dew point temperature so as to encourage condensation.

Question 2(c)

Give a geographical reason for each of the following:

(i) Condensation is the reverse process of evaporation.

(ii) Coasts receive more rainfall than the interior of the continents.

(iii) The windward sides of mountains receive more rainfall than the leeward sides.

Answer

(i) Condensation is the reverse process of evaporation as evaporation is the process by which water vapour enters the atmosphere on heating while condensation is the process by which water vapour is converted back to water droplets on cooling.

(ii) Coasts receive more rainfall than the interior of the continents because the humidity in the clouds is high when they are at the coast. When they reach the interior of the continents, they have already shed water in the form of rain, and so, they do not have much humidity left to cause rainfall.

(iii) The windward sides of mountains receive more rainfall than the leeward sides because 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.

Question 2(d)

Draw a well labelled diagram showing convectional rainfall.

Answer

Below labelled diagram shows convectional rainfall:

Question 3(a)

How is dew formed? What is the difference between fog and mist?

Answer

When water vapour condenses on the surface, it forms tiny droplets of water called dew.

The difference between fog and mist is as follows-

Question 3(b)

Describe briefly the orographic and convectional rainfall.

Answer

Orographic rainfall — It occurs from the cooling of warm moist air which ascends above the mountain barrier lying in the direction of the prevailing winds. The presence of mountains causes humid air to rise. The sudden ascent causes cooling of air, leading to condensation and precipitation.

Convectional rainfall — This type of rainfall is common in equatorial regions. The high temperature leads to the rapid heating of air. Such heated air rises in convectional currents, leading to development of clouds at about 10 km height. Ascending currents of hot and humid air causes condensation of the clouds, resulting in heavy rainfall.

Question 3(c)

Give a geographical reason for each of the following:

(i) A rain shadow area is generally dry.

(ii) Frontal rain is common in mid-latitudes.

(iii) Convectional rainfall is called 4 o'clock rainfall.

Answer

(i) 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.

(ii) Frontal rain is common in mid-latitudes due to the meeting of the sub-tropical and polar air masses. It is caused by convergence of two different air masses with different temperatures and other physical properties. When warm and cold air masses confront each other, the warmer air generally climbs above the colder air. The rising air is cooled while undergoing a frontal lift. This causes precipitation. Such precipitation is called cyclonic rainfall.

(iii) 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.

Question 3(d)

Define precipitation. Explain briefly the three forms of precipitation.

Answer

The process by which products of condensation, water droplets, ice crystals, sleet, etc., fall to ground is known as precipitation.

The three forms of precipitation are-

1. Rain — It is the most common form of precipitation. Raindrops of smaller size and less intensity are known as drizzle.

2. Snow — Water droplets which rise higher and freeze on account of drop in temperature is called snow. Snowfall usually occurs in winters in cold climates or on high mountains.

3. Hail — Sometimes, vertical air currents may push water droplets or ice particles higher. They form into solid ice and fall as hail. Hailstones cause great damage to crops.

Thinking Skills

Question 1

Condensation is regarded as the reverse process of evaporation. Imagine if this reverse process does not happen, what would be its consequences on climate and human beings? Also state the conditions under which this reversal may not happen.

Answer

If condensation does not occur, it would have significant consequences on climate and human beings:

Climate consequences —

1. Reduced cloud formation — Without condensation, clouds would be scarce or non-existent, leading to decreased cloud cover and overall cloud-related phenomena.
2. Decreased precipitation — The absence of condensation would result in limited or no rainfall, leading to drought conditions and water scarcity.
3. Disrupted water cycle — Condensation is a key component of the water cycle. Without condensation, the water cycle would be disrupted, affecting the distribution and availability of water resources.

Human consequences —

1. Water scarcity — The lack of condensation and subsequent reduced precipitation would result in water scarcity, affecting drinking water supplies, agriculture, and various industries dependent on water resources.
2. Impact agriculture and food production — Insufficient rainfall due to the absence of condensation would negatively impact agricultural productivity, leading to crop failures and food shortages.
3. Ecosystem disruption — Condensation plays a vital role in sustaining ecosystems by providing water for plants, animals, and other organisms. Without condensation, ecosystems would suffer from water stress, impacting biodiversity and ecological balance.

Possible conditions under which this reversal may not happen are:

1. Extremely low humidity — If the air has extremely low humidity levels, there may not be enough moisture present for condensation to occur.
2. Lack of condensation nuclei — In the absence of sufficient condensation nuclei, condensation may be hindered.
3. Absence of cooling mechanism — Lack of cooling, such as the ascent of air masses or interaction of warm and cold air, hindering condensation.

Question 2

Name two physical objects in your home which are affected by humidity. Also state the reason for such an affect.

Answer

Two physical objects in my home which are affected by humidity are:

1. Woodwind Musical Instruments like flutes are made of wood and can be impacted by humidity. High humidity can cause the wood to swell, affecting the instrument's structure, playability, and tone while low humidity can lead to the wood drying out, resulting in cracks, leaks, and changes in sound quality.
2. Electronic devices, such as computers, televisions and smartphones can be affected by humidity. High humidity levels can cause moisture to accumulate inside the devices, potentially leading to corrosion of circuitry and electrical components. Excessive humidity may also interfere with proper functioning and performance, causing malfunctions or even permanent damage.

Question 3

List two places which receive two types of rainfall. Give reasons to support your answer.

Answer

Two places which receive two types of rainfall are:

Western Ghats receive both orographic rainfall and convectional rainfall.

1. Moist winds from the Arabian Sea rise over the mountains, causing heavy orographic rainfall on the windward side.
2. High temperatures and local conditions lead to localized thunderstorms and convectional rainfall.

Northeastern states of Meghalaya and Assam also receive both orographic rainfall and convectional rainfall.

1. Moisture-laden winds from the Bay of Bengal encounter the Eastern Himalayas, resulting in significant orographic rainfall on the windward side.
2. Warm and humid conditions contribute to convective cloud formation, leading to heavy convectional showers and thunderstorms.

Project Work/Map Work

Question 1

List the forms of precipitation that occur in your city along with the time of year when they occur.

Answer

The forms of precipitation that occur in my city are:

1. Rain — Rainfall is most common during the monsoon season, which extends from June to September. The heaviest rainfall occurs in July and August.
2. Hail — Hailstorms are relatively rare in my city, but they can occur during the pre-monsoon months of March to May. These storms are more sporadic and less frequent compared to rainfall.
3. Fog, Mist and Dew — In winters, mornings are foggy in my city and there is a lot of dew at night.