Selina Concise Solutions for ICSE Class 9 Geography Chapter 15 Humidity

Exercises

I. Short Answer Questions.

Question 1. Define the following terms :
(a) Precipitation
(b) Evaporation
(c) Condensation
(d) Humidity
(e) Latent heat.
Answer:
(a) Precipitation - It is process by which condensation in different forms falling on the ground e.g. rainfall, snowfall, drizzle, sleet and hail etc.
(b) Evaporation - It is the process of converting water into water droplets and vapour.
(c) Condensation - It is the process of converting the water- droplets into water.
(d) Humidity - It is the amount of moisture present in the atmospheric air.
(e) Latent heat - It is the unseen heat absorbed by the atmospheric air to form vapour after reaching boiling point of \( 100^\circ C \) of water.
In simple words: These terms describe how water travels between the sky and the ground. Water turns into invisible gas (evaporation), then back into liquid or ice (condensation), and finally falls down as rain or snow (precipitation).

📝 Teacher's Note: Use the "Pot of Boiling Water" analogy. Steam rising is evaporation, the droplets on the lid are condensation, and the drips falling back are precipitation.

🎯 Exam Tip: For Latent Heat, remember to mention it is "unseen" or "hidden" heat that doesn't change the temperature but changes the state of water.

Question 2. What determines the amount of water vapour in the air?
Answer: The amount of water vapour or humidity is dependent on the temperature conditions, because the capacity of air to hold moisture changes according to the temperature, e.g., in higher temperature the water vapour amount may increase and in low temperature it may decrease.
In simple words: Temperature is the main boss. Hot air is like a big sponge that can hold lots of water, while cold air is like a tiny sponge that can only hold a little.

📝 Teacher's Note: Ask students if they feel stickier in summer or winter. This helps them realize that warmer air usually carries more moisture (humidity).

🎯 Exam Tip: Use the keyword "capacity" to explain how temperature affects the air's ability to hold moisture.

Question 3. How is relative humidity determined ?
Answer: Relative humidity is the percentage of water vapour with respect to the amount of air at a particular temperature.
\[ \text{Relative Humidity (RH)} = \frac{\text{Actual amount}}{\text{Water holding capacity}} \times 100 \]
In simple words: Relative humidity tells us how full of water the air is compared to how much it *could* hold. If it is \( 100\% \), the air is totally full and it might start to rain.

📝 Teacher's Note: Compare this to a glass of water. If a glass can hold \( 200 \text{ ml} \) but only has \( 100 \text{ ml} \), it is \( 50\% \) full. That \( 50\% \) is like relative humidity.

🎯 Exam Tip: Always write the formula clearly and mention that the result is expressed as a "percentage."

Question 4. Name four chief forms of condensation.
Answer: Four chief forms of condensation are clouds, fog, mist and dew droplets.
In simple words: Condensation happens when water vapor cools down. It can look like a fluffy cloud high up, or like fog, mist, and morning dew on the grass near the ground.

📝 Teacher's Note: Differentiate these by height: clouds are high, fog and mist are near the ground, and dew is on surfaces.

🎯 Exam Tip: If the question asks for "forms," listing just the names is enough for full marks.

Question 5. Mention the different forms of precipitation.
Answer: Different forms of precipitation are rainfall, drizzling, hailstones, snowfall and sleet etc.
In simple words: Precipitation is anything wet or icy that falls from the sky. It includes everything from light drizzle to heavy snow or hard balls of ice called hailstones.

📝 Teacher's Note: Explain that the form of precipitation depends on the temperature of the air as the water falls through it.

🎯 Exam Tip: "Rainfall" and "Snowfall" are the two most important forms to remember for your answer.

Question 6. What do you understand by ‘condensation nuclei’ ?
Answer: Condensation nuclei - Condensation nuclei is the base around which moisture is gathered and converts into a drop of water, e.g. the dust particles present in the atmosphere make the base of condensation form.
In simple words: Water vapor needs a "seat" to sit on to turn into a raindrop. Tiny bits of dust, salt, or smoke in the air act as these seats or "nuclei."

📝 Teacher's Note: Use the analogy of a "magnet" attracting water. Without these tiny particles, it would be much harder for clouds to form.

🎯 Exam Tip: Use "dust particles" as the standard example of a condensation nuclei.

Question 7. State the three types of rainfall.
Answer:
Relief Rainfall - It occurs from the cooling of warm moist air which ascends above the mountain barrier lying in the direction of the prevailing winds.
Cyclonic or Frontal Rainfall - It occurs when warm and cold air masses confront each other, the warmer air generally climbs above the colder air.
Convectional Rainfall - Ascending currents of hot and humid air causes condensation of the clouds, resulting in heavy rainfall.
In simple words: Rain happens in three ways: air being pushed up by mountains (Relief), air rising because it is hot (Convectional), or air being pushed up by a cold breeze (Cyclonic).

📝 Teacher's Note: Draw three simple diagrams on the board to show the "lifting" mechanism in each case, as "rising air" is the common factor.

🎯 Exam Tip: Learn the alternative name for Relief Rainfall, which is "Orographic Rainfall."

Question 8. What is cyclonic rainfall ?
Answer: Cyclonic rainfall is provided by the cyclones created in tropical and temperate regions along the air mass fronts, where warm and cold air meet together and the warm air is encircled by the cold air resulting in circular wind systems. The tropical cyclones provide heavy rainfall for a few days, but temperate cyclones provide light rainfall or drizzling for a long period.
In simple words: This rain happens when warm and cold air crash into each other. The warm air is forced to go up, where it cools and turns into rain.

📝 Teacher's Note: Explain that "fronts" are like the boundary lines between two different armies (air masses) clashing.

🎯 Exam Tip: Mention the difference between "tropical" (heavy) and "temperate" (light/long) cyclonic rain for a better score.

Question 9. How does latitude affect evaporation ?
Answer: Evaporation is highest in the tropical belt due to continuous vertical rays of the sun, while in temperate belt less evaporation and in polar belt least evaporation takes place due to less insolation.
In simple words: Latitude is about how close you are to the Equator. Near the Equator, the sun is very strong, so water evaporates very fast. Near the poles, it is cold, so evaporation is very slow.

📝 Teacher's Note: Remind students that "Insolation" refers to the heat received from the sun. More heat = More evaporation.

🎯 Exam Tip: Use the words "vertical rays" to describe why the tropics have high evaporation.

Question 10. Why is evaporation maximum in tropical deserts surrounded by seas ?
Answer: In tropical deserts, surrounded by seas, evaporation is maximum because of high temperatures and clear skies.
In simple words: Deserts are incredibly hot and have no clouds to block the sun. If they are near the sea, the sun can easily turn that seawater into vapor.

📝 Teacher's Note: Clear skies mean more sun hits the water directly. Without clouds, there's no "umbrella" to stop the heating.

🎯 Exam Tip: Mention "high temperatures" and "clear skies" as the two key reasons.

Question 11. State the factors favouring evaporation.
Answer: The conditions favourable for evaporation are high temperature and large amount of water of ocean, rainfall water etc.
In simple words: You need two main things for evaporation: heat and water. The more of both you have, the more evaporation you get.

📝 Teacher's Note: You can also mention "Dryness of air" and "Wind speed" as other factors that help water evaporate faster.

🎯 Exam Tip: "High temperature" is the most important factor to list first.

Question 12. What is the instrument used for measuring humidity?
Answer: Hygrometer or Dry and Wet Bulb Thermometer is used to measure humidity.
In simple words: Just like we use a thermometer for temperature, we use a special tool called a "Hygrometer" to see how much moisture is in the air.

📝 Teacher's Note: Show the students a picture of a Wet Bulb thermometer. Explain that the difference in temperature between the two bulbs tells us the humidity.

🎯 Exam Tip: Memorize the spelling of "Hygrometer" as it's a common one-word answer.

Question 13. State the process of clouds formation. Name the types of clouds.
Answer: When the water vapour converts into the water droplets floating in the air, the clouds are formed. Main types of clouds are Cirrus, Cumulus, Altus and Stratus.
In simple words: When invisible water gas cools down high in the sky, it turns into millions of tiny floating water drops. These groups of drops are what we see as clouds.

📝 Teacher's Note: Explain the shapes: Cirrus are wispy feathers, Cumulus are fluffy cotton balls, and Stratus are like flat grey blankets.

🎯 Exam Tip: Always list "Cirrus, Cumulus, and Stratus" as they are the primary types.

Question 14. Name the regions which receive rainfall only in summer.
Answer: The continental interiors in the sub-tropical regions get rainfall only in summer, e.g. Mangolia, Tibet etc.
In simple words: Places deep inside a continent, far from the sea, usually only get rain when the summer heat is strong enough to pull in moisture.

📝 Teacher's Note: Explain that these regions are far from the ocean's influence, so they don't get regular rain year-round.

🎯 Exam Tip: Use "Mangolia" or "Tibet" as your examples for summer rainfall regions.

Question 15. Name two regions of heavy rainfall.
Answer: Equatorial region and monsoon tropical region get highest rainfall. Highest rainfall is recorded in Cherrapunji and Mawsynram (\( 1080 \text{ cm} \)) in the world.
In simple words: The wettest places are near the Equator and places in India like Mawsynram, where it rains almost every day.

📝 Teacher's Note: Mention that Mawsynram is currently considered the wettest place on Earth. It gets more rain in a year than some deserts get in a century!

🎯 Exam Tip: Mention the specific measurement "\( 1080 \text{ cm} \)" to make your answer more precise.

Question 16. Describe the three chief ways in which condensation occurs.
Answer: Three chief ways to assist condensation are :
1. High amount of moisture present in atmosphere.
2. The elements providing the nuclei for it should be present in atmosphere, e.g., dust particles, salt and smoke etc.
3. The air should be saturated i.e. the relative humidity must be \( 100\% \) to create dew point or the temperature should be below dew point.
In simple words: For water gas to turn into liquid, the air must be very wet, there must be tiny dust particles to hold the water, and the air must cool down to its limit.

📝 Teacher's Note: "Saturated" means the air is completely "full" and cannot hold any more invisible water vapor.

🎯 Exam Tip: Mentioning the "\( 100\% \)" relative humidity or the "dew point" is essential for a scientific answer.

II. Give reasons for each of the following

Question 1. In Equatorial regions the sky often remains overcast with clouds.
Answer: Due to excessive heat the evaporation takes place in fast speed, and in every afternoon rainfall occurs after heavy cloud formation by convection process. So the sky mostly remains overcast with clouds.
In simple words: It is so hot at the Equator that water is constantly turning into clouds. By the afternoon, the clouds get so big and heavy that it almost always rains.

📝 Teacher's Note: This is known as "4 o'clock rain." The intense morning sun causes rapid rising air (convection), leading to daily afternoon storms.

🎯 Exam Tip: Use the word "convection" to describe why the air and moisture are rising.

Question 2. Human comfort depends on humidity.
Answer: Human efficiency is best at \( 40\% \) relative humidity. More or less humidity creates uneasiness of humidity and dryness.
In simple words: If the air is too wet (high humidity), our sweat won't dry and we feel sticky. If it is too dry, our skin and throat get itchy. We feel best right in the middle.

📝 Teacher's Note: Explain that on very humid days, our body's natural cooling system (sweating) stops working well because the air is already too full of water.

🎯 Exam Tip: Mention the specific figure of "\( 40\% \)" as the ideal comfort level.

Question 3. Condensation is the reverse process of evaporation.
Answer: Condensation takes place upto the dew-point comes, but after it precipitation starts due to water-droplets converted into water drops. So, condensation and precipitation are different processes occurring in different conditions and temperature episodes.
In simple words: Evaporation turns water into gas. Condensation does the opposite—it turns the gas back into water. They are like a two-way street.

📝 Teacher's Note: Evaporation happens when you add heat; condensation happens when you remove heat (cooling).

🎯 Exam Tip: Define both briefly to show how one "undoes" what the other "did."

Question 4. Coasts receive more rainfall than the interior of the continents.
Answer: Moisture-laiden winds provide more rainfall to the coastal parts due to being situated by the coast and receiving the rain bearing winds, but the interior get negligible rainfall due to being the almost dry winds without moisture.
In simple words: The ocean is the source of all rain. Coastal areas are right next to the source, but by the time the wind reaches the deep interior, it has already "dropped" all its rain.

📝 Teacher's Note: This is like a sponge being carried across a room. It drips the most water right where you pick it up (the coast) and is dry by the time you reach the other side.

🎯 Exam Tip: Use the phrase "moisture-laden winds" to describe the winds coming from the ocean.

Question 5. The windward sides of mountains receive more rainfall than the leeward sides.
Answer: The windward sides of mountainous slopes get ample rainfall by striking with the rain bearing winds first, while the leeward sides cannot get sufficient rainfall due to being on other side where the winds become almost dry due to imparting rainfall in windward due to loss of major part of moisture and water drops.
In simple words: When wet wind hits a mountain, it is forced to go up and drop its rain on that side. By the time the wind climbs over to the other side (the leeward side), it has no water left.

📝 Teacher's Note: The leeward side is often called a "Rain Shadow Area." It can be a desert even if the other side of the mountain is a rainforest.

🎯 Exam Tip: Contrast the "Windward" side (where wind hits) with the "Leeward" side (the sheltered back side).

III. Match the following

IV. Long Answer Questions.

Question 1. Distinguish between Absolute Humidity and Relative Humidity.
Answer:
Absolute Humidity :
1. It is the measure of the actual amount of water vapour in the air, regardless of temperature.
2. It is expressed as grams of moisture per cubic meter of air (\( g/m^3 \)).
3. The higher the amount of water vapour, the higher is the absolute humidity.
4. In weather calculations, absolute humidity is generally not taken into account.
Relative Humidity:
1. It measures water vapour in air but relative to the maximum vapour that the air can hold at that temperature.
2. It is expressed as the ratio (percentage value) 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.
3. Warm air possesses more water vapour than cold air, so with the same amount of absolute humidity, air will have a different relative humidity depending on temperature.
4. It is the essential characteristic of weather forecasts, which indicates the likelihood of precipitation, dew or fog.
In simple words: Absolute humidity is just the total weight of water in the air. Relative humidity is a percentage that tells us how close the air is to being "full." Relative humidity is more useful for predicting rain.

📝 Teacher's Note: Absolute is like saying "I have \( 5 \text{ kg} \) of apples." Relative is like saying "My basket is \( 50\% \) full." Weather reporters always use the "basket full" (Relative) version.

🎯 Exam Tip: Note the units: Absolute is "\( g/m^3 \)" and Relative is a "\( \% \)."

Question 2. With reference to condensation, define the following :
(a) Process of condensation.
(b) Atmospheric conditions that favour condensation.
(c) Forms of Condensation.
Answer:
(a) Condensation is the reverse process of evaporation. In condensation, water vapour in the atmosphere get converted into water droplets or ice. Condensation takes place when water vapour is added to saturated air or when the temperature falls below the temperature at which air become saturated.
(b) 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.
(c) Forms of condensation : Following are the forms of the
• condensation : Dew, frost, fog, mist, white frost and clouds. The clouds are formed when the temperature falls down below dew points, while dew, fog and clouds are formed when the temperature remains higher than the freezing point.
• Clouds : Clouds are formed when minute droplets of water vapour condense on a nuclei and remain suspended in air.
• Dew : When water vapour condenses on the surface, it forms tiny droplets of water called dew. Dew commonly occurs during winter on account of cooling of air below dew point.
• Frost : In very low temperature, when condensation occurs at zero metre or ground level, water vapour freezes into minute crystals of ice on objects near the ground such as blades of grass, leaves and tiny rock particles. Frost is harmful to plants.
In simple words: Condensation turns gas back to liquid when it gets cold. It needs dust to stick to and wet air. It can show up as clouds in the sky or as dew and frost on the ground.

📝 Teacher's Note: Emphasize that "Dew Point" is the magic temperature where condensation starts. If the air is cooler than this point, we get liquid water.

🎯 Exam Tip: For part (b), listing "High water vapour," "Condensation nuclei," and "Cooling below dew point" are the three required points.

PQ. Describe the process of evaporation together with factors that favour it.
Answer: For evaporation excessive heat and presence of water bodies is essential. Nearly \( 600 \text{ calories} \) of heat is required to change water into water vapour. Evaporation is maximum in tropical belt and mainly in hot desert region surrounded by water bodies. In the equatorial belt, due to overcast with clouds, evaporation is comparatively less due to obstacles of cloud in heating process.
In simple words: Evaporation happens when water gets enough heat to turn into invisible gas. It happens fastest in hot, sunny deserts near the ocean.

📝 Teacher's Note: Explain that even though the Equator is hot, it has many clouds that block the sun, so deserts actually have higher evaporation than the rainy Equator.

🎯 Exam Tip: Mention that "\( 600 \text{ calories} \)" of heat are needed for evaporation as a specific scientific detail.

Question 3. Name the three types of rainfall. With the help of a diagram describe each type of rainfall.
Answer:
1. Convectional rainfall : It occurs in the 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 \( 10 \text{ km} \) height. Ascending currents of hot and humid air causes condensation of the clouds, resulting in heavy rainfall. 2. Relief Rainfall : Relief rainfall is also known as 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. 3. Cyclonic Rainfall : This type of rainfall is due to cyclones and depressions. When warm and cold air masses confront each other, the warmer air generally climbs above the colder. The rising air is cooled while undergoing a frontal lift. This causes precipitation.
In simple words: Convectional rain comes from heat rising. Relief rain comes from mountains pushing air up. Cyclonic rain comes from warm air sliding over cold air.

📝 Teacher's Note: The key for all three is "Rising Air." Air must go up to cool down and make rain. The only difference is what "pushes" it up (Heat, Mountains, or Cold Air).

🎯 Exam Tip: Draw the mountain for Relief rain and show the rain on only one side—the "Windward" side.

Question 4. Define precipitation. Write short notes on three forms of precipitation.
Answer: The process by which products of condensation, viz water droplets, ice crystals, sleet, etc., fall to ground is known as precipitation. Rainfall, snowfall, drizzle, sleet and hail are the chief forms of precipitation. Precipitation takes place only when they particles of water join together to form large sized particles which become too heavy to remain in suspension in the cloud.
1. Rain : It is the most common form of precipitation. Raindrops of smaller size and less intensity are known as drizzle.
2. Dew : When water vapour condenses on the surface, it forms tiny droplets of water called dew. Dew commonly occurs during winter on account of cooling of air below dew point.
3. Frost : In very low temperature, when condensation occurs at zero metre or ground level, water vapour freezes into minute crystals of ice on objects near the ground such as blades of grass, leaves and tiny rock particles. Frost is harmful to plants.
In simple words: Precipitation is water falling from clouds when it gets too heavy to stay up. It falls as liquid rain, cold morning dew, or frozen icy frost.

📝 Teacher's Note: Note that the textbook answer includes "Dew" and "Frost" as forms of precipitation, although they are technically forms of condensation because they don't "fall" from the sky.

🎯 Exam Tip: When writing about rain, mention that smaller drops are called "drizzle" for extra detail.

Question 6. Make a brief survey of the world distribution of rainfall.
Answer: Equatorials and coastal areas of monsoon countries get maximum rainfall, more than \( 200 \text{ cm} \), sub-tropical areas get moderate rainfall \( 100 - 200 \text{ cm} \), and the least rainfall areas are Hot and cold deserts getting nearly \( 25 \text{ cm} \).
In simple words: Rainfall is not even. The middle of the world (Equator) and coasts get the most, middle regions get a medium amount, and deserts get almost none.

📝 Teacher's Note: Use a world map to show that rainfall decreases as you move away from the Equator or move deeper into the middle of a large continent.

🎯 Exam Tip: Remember the three levels: High (\( >200 \text{ cm} \)), Moderate (\( 100-200 \text{ cm} \)), and Low (\( \approx 25 \text{ cm} \)).