Humidity - Questions & Answers

1. Name the heat that is lost during evaporation and passes into water vapour in a hidden form and is released in the atmosphere during condensation.
(a) Condensed heat    (b) Humidity    (c) Latent heat    (d) Relative Humidity
Answer: (c) Latent heat

2. Which, amongst the following, is NOT one of the factors favouring evaporation?
(a) Humidity    (b) Supply of heat    (c) Winds    (d) Precipitation
Answer: (d) Precipitation

3. 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:
(a) Humidity    (b) Dew Point    (c) Relative humidity    (d) Latent heat
Answer: (c) Relative humidity

4. The temperature at which air gets fully saturated:
(a) Humidity    (b) Dew Point    (c) Relative humidity    (d) Latent heat
Answer: (b) Dew Point

5. Assertion (A): Under conditions of high relative humidity, the rate of evaporation of sweat from the skin decreases and the human being feels warm and uncomfortable.
Reason (R): The human body dissipates heat through perspiration and its evaporation.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.

6. The measure of the actual amount of water vapour in the air, regardless of temperature:
(a) Absolute Humidity    (b) Humidity    (c) Dew Point    (d) Relative Humidity
Answer: (a) Absolute Humidity

7. The process by which products of condensation, viz. water droplets, ice crystals, sleet etc. fall to the ground:
(a) Evaporation    (b) Humidation    (c) Precipitation    (d) Condensation
Answer: (c) Precipitation

8. Which of the following type of cloud has a cauliflower-like shape?
(a) Cirrus    (b) Cumulus    (c) Strata    (d) None of the above
Answer: (b) Cumulus

9. Condensation nuclei are
(a) impurities that support condensation.
(b) water particles that help in precipitation.
(c) droplets formed as a result of condensation.
(d) droplets that fall to the ground.
Answer: (a) impurities that support condensation.

10. Which of the following is incorrect
(a) Frontal rainfall : cyclones
(b) Convectional rainfall : 4 o'clock showers
(c) Cyclonic rainfall : mountains
(d) Relief rainfall : mountain barriers
Answer: (c) Cyclonic rainfall : mountains

11. In the month of August after many rainy days there was a clear Sunday. We went for a picnic to a park. We felt so hot and uncomfortable that we changed plans and went to watch a movie instead. What caused us this discomfort?
(a) Latent heat released as a result of condensation raised the temperature.
(b) High humidity due to the rains of the previous day.
(c) Heat released from the surface of the earth raised the temperature.
(d) None of the above.
Answer: (b) High humidity due to the rains of the previous day.

12. Jyoti and her family had gone to the Little Andaman Island for a holiday. It was a clear day when the sky became dark with clouds and there was heavy rain late in the afternoon. This was the case every day that they spent there. What type of rainfall is this?
(a) Relief    (b) Convectional    (c) Cyclonic    (d) Frontal
Answer: (b) Convectional

1. What determines the amount of water vapour in the air?
Answer: The amount of water vapour in the air is primarily determined by temperature. Higher temperatures increase the capacity of the air to hold moisture. It also depends on factors favoring evaporation such as dry air, supply of heat, and strong winds.

2. How is relative humidity determined?
Answer: Relative humidity is determined by calculating the ratio between the actual amount of water vapour in a given mass of air (Absolute Humidity) and the maximum water holding capacity of that air at the same temperature. It is calculated using the formula: (Actual amount / Water holding Capacity) × 100, and is typically measured using a Hygrometer (Dry and Wet Bulb Thermometer).

3. Name four chief forms of condensation.
Answer: The four chief forms of condensation are clouds, dew, frost, and fog (or mist).

4. Mention the different forms of precipitation.
Answer: The different forms of precipitation include rain, drizzle, snow, and hail (or sleet).

5. Give one difference between fog and mist.
Answer: Mist is less dense and dissipates more quickly than fog. During fog, visibility extends to less than one kilometre, whereas under mist conditions, visibility may go up to two kilometres.

6. What do you understand by 'condensation nuclei'?
Answer: Condensation nuclei are minuscule solid particles present in the air, such as dust, salt, or smoke, around which water vapour condenses to form droplets. Without these impurities, condensation cannot take place.

7. State the three types of rainfall.
Answer: The three types of rainfall are Relief (Orographic) Rainfall, Convectional Rainfall, and Cyclonic (Frontal) Rainfall.

8. Why is orographic rainfall also called relief rainfall?
Answer: Orographic rainfall is also called relief rainfall because it is directly caused by the physical relief of the land. When a mountain or highland barrier (a relief feature) lies in the path of warm, moist winds, it forces the air to ascend, cool, and condense, causing rain.

9. What is cyclonic rainfall? What are fronts?
Answer: Cyclonic rainfall is the precipitation caused when two different air masses with varying temperatures and properties converge, forcing the lighter, warm air to climb over the colder, heavier air, leading to cooling, condensation, and rain. Fronts are the boundary zones where these two distinct air masses (warm and cold) confront and meet each other.

(a) Precipitation
Answer: The process by which products of condensation, namely water droplets, ice crystals, sleet, etc., fall to the ground after particles join together and become too heavy to remain suspended in the clouds.

(b) Evaporation
Answer: The process by which liquid water enters the atmosphere by transforming into a gaseous state (water vapour) upon heating.

(c) Condensation
Answer: The reverse process of evaporation, where water vapour in the atmosphere gets converted into liquid water droplets or solid ice upon cooling.

(d) Humidity
Answer: The general term denoting the amount of water vapour present in the air.

1. (a) What is 'humidity'? How is humidity measured?
Answer: Humidity is the amount of water vapour present in the air. It is measured using an instrument called a Hygrometer, also known as a Dry and Wet Bulb Thermometer. A difference in temperature readings between the dry bulb and the water-cooled wet bulb indicates the relative humidity of the atmosphere.

1. (b) Distinguish between Absolute Humidity and Relative Humidity.
Answer: Absolute Humidity is the actual measure of the mass or weight of water vapour held by air at a certain temperature and volume (expressed in g/m³). Relative Humidity is the ratio, expressed as a percentage, between the absolute humidity of a given mass of air and the maximum amount of water vapour it can hold at that same temperature.

1. (c) Give a geographical reason for each of the following:
(i) The total volume of water in the oceans and seas remains constant.
Answer: The volume remains constant because all the water that evaporates from the earth's water bodies is eventually returned to them directly through the processes of condensation and precipitation, and indirectly via streams and surface runoffs.

(ii) In Equatorial regions the sky often remains overcast with clouds.
Answer: High temperatures in the Equatorial regions lead to the rapid daily heating of air. This heated, moisture-laden air rises continuously in convectional currents, expanding and cooling at higher altitudes to cause heavy condensation and persistent cloud cover.

(iii) When relative humidity is 100% the temperature reading on both wet and dry thermometers is the same.
Answer: When relative humidity is 100%, the air is fully saturated and cannot hold any more water vapour. Consequently, no evaporation takes place from the wet cloth tied around the wet bulb. Without evaporation absorbing latent heat, there is no cooling effect, resulting in identical readings on both thermometers.

1. (d) Draw a well labelled diagram showing orographic rainfall.
Answer: [Note for student: Please draw a mountain showing warm, moist air ascending the windward slope, forming clouds, and raining heavily. Then show dry air descending on the opposite, leeward slope creating a 'Rain shadow area'. Refer to Fig. 15.6 in the chapter for the exact diagram.]

2. (a) What is condensation? Explain briefly the process of condensation.
Answer: Condensation is the reverse process of evaporation, where invisible water vapour in the atmosphere converts into water droplets or ice. The process occurs when water vapour is continuously added to saturated air, or when the air temperature falls below its dew point, forcing the extra moisture to shed around microscopic impurities like dust or smoke.

2. (b) Explain the atmospheric conditions that favour condensation.
Answer: The three main atmospheric conditions favoring condensation are: (1) The presence of a high amount of water vapour in the atmosphere. (2) The temperature of the air falling below the dew point to encourage saturation. (3) The presence of minuscule particles of dust, salt, or smoke to act as condensation nuclei for the moisture to gather around.

2. (c) Give a geographical reason for each of the following:
(i) Condensation is the reverse process of evaporation.
Answer: Evaporation involves absorbing heat to change liquid water into gaseous water vapour. Condensation does the exact opposite; it cools the gaseous water vapour to turn it back into liquid or solid droplets, releasing the stored latent heat back into the atmosphere in the process.

(ii) Coasts receive more rainfall than the interior of the continents.
Answer: Coastal areas are situated next to large bodies of water, giving them direct access to moisture-laden maritime winds. As these winds move inland, they drop most of their moisture near the coasts due to relief barriers or coastal convection, becoming increasingly dry by the time they reach the interior of continents.

(iii) The windward sides of mountains receive more rainfall than the leeward sides.
Answer: Moisture-carrying winds are forced upward by the mountain on the windward side, causing the air to cool, condense, and drop heavy relief rainfall. By the time the winds cross the peak and descend the leeward side, they have lost most of their moisture, and the descending motion warms and compresses the air, preventing further rain.

2. (d) Draw a well labelled diagram showing convectional rainfall.
Answer: [Note for student: Please draw flat ground showing heated air rising vertically as 'warm air' arrows, leading up to large, tall cumulus clouds at roughly 10km height, and heavy rain accompanied by lightning falling down. Refer to Fig. 15.7 in the chapter.]

3. (a) How is dew formed? What is the difference between fog and mist?
Answer: Dew is formed when air cools below its dew point, typically during cold winter nights, causing water vapour to condense directly onto cool surface objects like grass blades and leaves in the form of tiny droplets. The main difference between fog and mist is density and visibility. Mist is less dense and dissipates quickly (visibility up to 2 km), while fog is much denser with water droplets suspended very close to the earth's surface (visibility less than 1 km).

3. (b) Describe briefly the orographic and convectional rainfall.
Answer: Orographic rainfall occurs when warm, moist air is obstructed by a mountain barrier and forced to rise. The ascent cools the air, leading to condensation and heavy rainfall on the mountain's windward side. Convectional rainfall occurs primarily in equatorial regions where intense daily heat warms the ground rapidly. The heated air rises in vertical convection currents, cooling at high altitudes to form towering clouds that unleash heavy showers, often with thunder and lightning.

3. (c) Give a geographical reason for each of the following:
(i) A rain shadow area is generally dry.
Answer: A rain shadow area is dry because it is located on the leeward side of a mountain. Winds descending this slope have already shed their moisture on the windward side. As the air drops in altitude, it gets compressed and warmed, decreasing its relative humidity and ending the chances of precipitation.

(ii) Frontal rain is common in mid-latitudes.
Answer: Mid-latitudes act as the primary meeting ground for contrasting air masses—warm tropical air from the lower latitudes and cold polar air from the higher latitudes. The convergence of these different air masses creates 'fronts' where the warm air is lifted over the cold air, leading to frequent cyclonic or frontal rainfall.

(iii) Convectional rainfall is called 4 o'clock rainfall.
Answer: In hot equatorial regions, intense heating causes hot and humid air to rise continuously throughout the morning and early afternoon. By late afternoon, typically around 4 O'clock, the accumulated condensation of these ascending clouds reaches a tipping point, resulting in heavy, predictable daily downpours.

3. (d) Define precipitation. Explain briefly the three forms of precipitation.
Answer: Precipitation is the process where products of condensation join together, become too heavy to remain suspended in clouds, and fall to the earth. The three main forms are: (1) Rain: The most common form consisting of liquid water droplets falling to the ground (lighter forms are called drizzle). (2) Snow: Formed when water droplets rise to higher altitudes, freeze due to dropping temperatures, and fall as ice flakes in cold climates. (3) Hail: Occurs when strong vertical air currents push droplets or ice particles higher into the freezing zone, turning them into solid ice before falling to the earth, often damaging crops.

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 never happened, clouds would never form, completely stopping the water cycle. There would be zero precipitation (no rain or snow), leading to widespread catastrophic droughts. Rivers and lakes would dry up, vegetation would die, and human beings, along with all terrestrial life, would face extinction due to a lack of fresh drinking water and food. The global climate would become drastically hotter and drier. This reversal may not happen if the air lacks 'condensation nuclei' (like dust or smoke) for the water to cling to, or if the atmospheric temperature never drops below the dew point to allow the air to become saturated.

2. Name two physical objects in your home which are affected by humidity. Also state the reason for such an affect.
Answer: (1) Wooden doors and furniture: Wood is porous and naturally absorbs moisture from highly humid air, causing it to swell up and making doors difficult to open or close during the rainy season. (2) Kitchen salt or sugar: These substances are hygroscopic, meaning they readily absorb water vapour from the humid air, causing them to clump together and become sticky.

3. List two places which receive two types of rainfall. Give reasons to support your answer.
Answer: (1) The Western Ghats of India: This region receives heavy Orographic rainfall from the South-West monsoon winds striking the mountains, but it also experiences Cyclonic rainfall resulting from tropical depressions originating in the Arabian Sea. (2) The Eastern Coastal Plains of India (e.g., Tamil Nadu coast): This region occasionally receives Convectional rainfall during hot summer days due to intense localized heating, while also heavily relying on Cyclonic rainfall brought by retreating monsoons and tropical cyclones from the Bay of Bengal during the winter.

List the forms of precipitation that occur in your city along with the time of year when they occur.
Answer: [Note for student: This answer depends on your specific city in India. For example, if you live in Mumbai or Delhi, you primarily experience 'Rain' from June to September due to the Monsoons. You may also experience 'Dew' or light 'Fog' during the cooler winter mornings between December and February. If you live in a high-altitude Himalayan city like Shimla, you would list 'Snow' occurring between December and February, alongside summer rains.]