NCERT Class 11 Geography Fundamental of Physical Geography: Chapter 10 — C H A P T E R
This chapter, "Water in the Atmosphere," from NCERT's Fundamental of Physical Geography for Class 11, details the crucial role of water vapor in atmospheric phenomena. It explains evaporation, the transformation of liquid water to gas driven by heat, and condensation, the reverse process where water vapor turns into liquid or solid due to cooling. The chapter defines humidity, including absolute and relative humidity, and discusses factors influencing them like temperature and air movement. It also covers various forms of condensation such as dew, frost, fog, mist, and clouds, classifying clouds into cirrus, cumulus, stratus, and nimbus types based on their altitude and appearance. Understanding these processes is vital for comprehending weather patterns and climate.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Geography |
| Book | Fundamental of Physical Geography |
| Chapter | Chapter 10 — C H A P T E R |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 6 minutes |
| Word count | 1189 |
Learning outcomes
- Understand the forms of water in the atmosphere (gaseous, liquid, solid).
- Explain the processes of evaporation and condensation.
- Define and differentiate between absolute and relative humidity.
- Identify and describe various forms of condensation: dew, frost, fog, mist, and clouds.
- Classify clouds based on their altitude and appearance (cirrus, cumulus, stratus, nimbus).
Vocabulary
| Word | Meaning |
|---|---|
| Evaporation | The process by which water is transformed from liquid to gaseous state. |
| Condensation | The transformation of water vapour into water. |
| Humidity | Water vapour present in the air. |
| Absolute Humidity | The weight of water vapour per unit volume of air. |
| Relative Humidity | The percentage of moisture present in the atmosphere compared to its full capacity at a given temperature. |
| Dew Point | The temperature at which saturation occurs in a given sample of air. |
| Dew | Moisture deposited in the form of water droplets on cooler surfaces. |
| Frost | Condensation taking place below freezing point, forming ice crystals. |
| Fog | A cloud with its base at or very near to the ground, reducing visibility. |
| Mist | Similar to fog but contains more moisture and reduces visibility less. |
| Clouds | A mass of minute water droplets or tiny ice crystals formed by condensation in free air at considerable elevations. |
| Hygroscopic Condensation Nuclei | Very small particles in free air around which condensation occurs. |
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Practice questions
- What is evaporation? Answer: Evaporation is the process by which water transforms from a liquid to a gaseous state, primarily driven by heat.
- Define condensation. Answer: Condensation is the process where water vapor in the air changes into liquid water or ice crystals.
- What is the difference between absolute humidity and relative humidity? Answer: Absolute humidity is the actual amount of water vapor in a volume of air, while relative humidity is the percentage of moisture present compared to the air's maximum capacity at a given temperature.
- Under what conditions does dew form? Answer: Dew forms when moisture is deposited as water droplets on cooler surfaces, typically under clear skies, calm air, high humidity, and long, cold nights, with the dew point above freezing.
- Name the four main types of clouds. Answer: The four main types of clouds are cirrus, cumulus, stratus, and nimbus.
Practice MCQs
Q1. What is the primary cause of evaporation?
Explanation: Heat is the main cause for evaporation, as it provides the energy needed to transform liquid water into water vapor.
Q2. Which term refers to the amount of water vapor present in the atmosphere as a percentage of its full capacity?
Explanation: Relative humidity expresses the amount of moisture in the air as a percentage of the maximum it can hold at a specific temperature.
Q3. Condensation occurs when:
Explanation: Condensation happens when moist air cools to a point where it can no longer hold all its water vapor, causing it to change into liquid or solid form.
Q4. Which type of cloud is characterized by a thin, detached, and feathery appearance at high altitudes?
Explanation: Cirrus clouds are high-altitude clouds known for their thin, wispy, and feathery appearance, typically composed of ice crystals.
Q5. Fog is essentially:
Explanation: Fog is defined as a cloud that forms at or very close to the Earth's surface, significantly reducing horizontal visibility.
Q6. When condensation takes place below the freezing point (0°C), forming ice crystals, it is called:
Explanation: Frost forms when the dew point is at or below freezing, causing excess moisture to deposit as ice crystals on cold surfaces.
Frequently asked questions
What is the role of water vapor in the atmosphere?
Water vapor plays a crucial role in weather phenomena, contributing to processes like evaporation, condensation, and precipitation, and influencing temperature and humidity.
How does temperature affect the air's capacity to hold water vapor?
As air temperature increases, its capacity to hold water vapor also increases. Conversely, cooler air can hold less moisture.
What are condensation nuclei?
Condensation nuclei are tiny particles (like dust, smoke, or salt) in the atmosphere that provide surfaces for water vapor to condense upon.
What is the main difference between fog and mist?
Fog is a cloud at ground level that reduces visibility to less than 1 km, while mist also reduces visibility but contains more moisture and limits it to between 1 km and 2 km.
How are clouds classified?
Clouds are classified into four main types based on their height, expanse, density, and transparency: cirrus, cumulus, stratus, and nimbus.
What are the ideal conditions for dew formation?
Ideal conditions for dew include clear skies, calm air, high relative humidity, and long, cold nights, with the dew point above freezing.
What is the dew point?
The dew point is the temperature at which the air becomes saturated and excess water vapor begins to condense.
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NCERT Class 11 Geography — Fundamental of Physical Geography — Chapter 10 — C H A P T E R. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.