GEOGRAPHY- CLASS-11: FUNDAMENTALS OF PHYSICAL GEOGRAPHY
CHAPTER-10
Water in the Atmosphere
1. Multiple Choice Questions
(i) Which one of the following is the most important constituent of the atmosphere for human beings?
Answer: (d) Oxygen
Explanation:
Oxygen is the most important constituent of the atmosphere for human beings because it is essential for respiration. Humans and animals inhale oxygen to release energy from food through the process of cellular respiration. Without oxygen, life on Earth would not be possible. Oxygen also supports combustion and many biological processes.
(ii) Which one of the following process is responsible for transforming liquid into vapour?
Answer: (c) Evaporation
Explanation:
Evaporation is the process in which liquid water changes into water vapour due to the heat of the Sun. It is an important part of the water cycle and helps in cloud formation and precipitation.
(iii) The air that contains moisture to its full capacity:
Answer: (d) Saturated air
Explanation:
Saturated air is the air that holds the maximum amount of water vapour possible at a given temperature. Any further cooling or addition of moisture results in condensation.
(iv) Which one of the following is the highest cloud in the sky?
Answer: (a) Cirrus
Explanation:
Cirrus clouds are the highest clouds in the atmosphere. They usually occur at an altitude of about 6 km to 12 km. These clouds are thin, white and feathery in appearance and are mainly composed of ice crystals.
2. Answer the following questions in about 30 words.
(i) Name the three types of precipitation.
Answer:
The three main types of precipitation are:
- Convectional precipitation
- Orographic (Relief) precipitation
- Cyclonic (Frontal) precipitation
These types differ according to the process through which moist air rises, cools and condenses.
(ii) Explain relative humidity.
Answer:
Relative humidity is the ratio between the actual amount of water vapour present in the air and the maximum amount of water vapour the air can hold at the same temperature. It is expressed as a percentage.
Formula:
Relative Humidity = (Actual Water Vapour ÷ Maximum Water Vapour Capacity) × 100
When the relative humidity reaches 100%, the air becomes saturated and condensation begins.
(iii) Why does the amount of water vapour decrease rapidly with altitude?
Answer:
Most water vapour enters the atmosphere through evaporation from oceans, rivers, lakes and land surfaces. Since these sources are located near the Earth's surface, the amount of water vapour decreases rapidly with increasing altitude. In addition, lower temperatures at higher altitudes reduce the air's capacity to hold moisture.
(iv) How are clouds formed? Classify them.
Answer:
Clouds are formed when warm, moist air rises, expands and cools to its dew point. Water vapour then condenses around tiny dust particles, forming tiny water droplets or ice crystals that make clouds.
Clouds are classified into four main types:
- Cirrus: High, thin and feathery clouds.
- Cumulus: White, fluffy clouds with flat bases.
- Stratus: Low, uniform grey clouds covering large areas.
- Nimbus: Thick, dark rain-bearing clouds.
3. Answer the following questions in about 150 words.
(i) Discuss the salient features of the world distribution of precipitation.
Answer:
The distribution of precipitation over the world is highly uneven and depends upon latitude, atmospheric circulation, distance from the sea, relief and ocean currents. The Equatorial region receives the highest rainfall throughout the year due to intense heating and convectional rainfall. Tropical monsoon regions receive heavy seasonal rainfall. The subtropical high-pressure belts around 30° North and South are generally dry because descending air prevents cloud formation, leading to deserts such as the Sahara and Arabian Deserts. Temperate regions receive moderate rainfall mainly from cyclonic disturbances. Coastal regions generally receive more rainfall than inland areas because they are closer to the source of moisture. Windward slopes of mountains receive heavy orographic rainfall, while leeward slopes remain dry and form rain-shadow regions. Polar regions receive very little precipitation because of extremely low temperatures and limited evaporation. Thus, rainfall varies greatly from one region to another depending on physical and climatic conditions.
(ii) What are forms of condensation? Describe the process of dew and frost formation.
Answer:
Condensation is the process by which water vapour changes into liquid water or ice when air becomes saturated. The main forms of condensation are dew, frost, fog, mist and clouds.
Dew forms on clear and calm nights when the Earth's surface loses heat through radiation. If the surface cools below the dew point but remains above 0°C, water vapour condenses into tiny water droplets on grass, leaves and other objects.
Frost forms when the surface temperature falls below 0°C. Instead of forming water droplets, water vapour changes directly into tiny ice crystals through deposition. Frost commonly occurs during cold winter nights in temperate and mountainous regions.
Both dew and frost form due to cooling of the Earth's surface, but dew forms as liquid water while frost forms as ice crystals.