Important Questions: Water in the Atmosphere | Geography Class 11 - Humanities/Arts PDF Download

Very Short Answer Type Questions

Q1: What is meant by humidity?
Ans: The state of the atmosphere with respect to its content of moisture or water vapour is called humidity.

Q2: Name three states in which water exists.
Ans: Water exists in three states or forms:

• Solid (ice),
• Liquid (water),
• Gas (water vapour).

Q3: What is the dew point?
Ans: It is the temperature at which air, on cooling, becomes saturated with water vapour, and below which condensation begins and dew forms.

Q4: Identify various forms of precipitation.
Ans: Various forms of precipitation include rainfall, snowfall, hail, sleet and drizzle.

Q5: How does precipitation take place?
Ans: Precipitation takes place as a result of the continued condensation and growth of the moisture particles until they become too large to remain suspended in the air.

Q6: Which factors control evaporation?
Ans: There are three main factors which control evaporation:

• aridity,
• temperature,
• movement of air.

Q7: What are the different types of fog?
Ans: Fogs are of three types: radiating, advection and frontal fog.

Q8: What are the different types of rainfall?
Ans: Rainfall is of three types: convectional, orographic and cyclonic rainfall.

Short Answer Type Questions

Q9: What is relative humidity and how is it measured?
Ans: The amount of water vapour in the air compared with the amount that would be present if the air was saturated at that temperature. It is expressed in percentage determined by dividing the absolute humidity by water holding capacity of air. If the air is saturated, its relative humidity is 100%; if only half saturated, the relative humidity. is 50%. Since the capacity of air for absorbing and retaining moisture varies with temperature, the relative humidity of air mass can be altered by merely lowering its temperature without changing the actual amount of moisture present in it.

Q10: What are the middle clouds?
Ans: The clouds which form at height of2000-7000 km. above the ground are called middle clouds. Altostratus and altocumulus are examples.

• Altostratus – It is a uniform sheet of cloud, grey or bluish in colour and usually has a fibrous structure.
• Altocumulus – These are flattened globular masses of clouds arranged in lines or waves. They have large globules with shadows.

Q11: What is condensation and how does it take place?
Ans: Condensation is the process of water vapour changing to a liquid state. If the air is cooled below its dew point, some of the air’s water vapour becomes liquid. Thus, any amount of cooling of saturated air starts the process of condensation. Condensation may start with the addition of any further water vapour to the saturated air, or with the reduction of its temperature.

Q12: What are the effects of humidity?
Ans: The main effects of humidity are:

• The skin of the human body starts to crack due to low relative humidity.
• It causes joint pain in the human body.
• The high relative humidity is harmful to the human body.
• The joints of furniture get loosened.

Q13: How is rainfall caused?
Ans: The moist air is cooled, saturated and condensation takes place. Water vapour condenses on a large number of dust particles to form clouds. The cloud droplets merge to form raindrops. When these raindrops become so heavy that air cannot hold them, these fall on the earth in the form of rainfall. The release of moisture in the form of drops of water is called rainfall.

Long Answer Type Questions

Q14: Describe the factors controlling the rate of evaporation and evapotranspiration.
Ans: vaporation is the process by which liquid water or ice changes into water vapour. It occurs whenever energy is transported to an evaporated surface and temperature rises. The molecules become more mobile and overcome the forces binding them to the water surface and break away resulting in evaporation. Evapotranspiration, on the other hand, is the amount of moisture transferred to the atmosphere by evaporation of liquid and solid water plus transpiration from living tissues principally from the plants.
Factors like the temperature of the air, source of moisture, vegetation cover, latitude, permeability and water retention effect evaporation and evapotranspiration. Evaporation depends upon air temperature. Greater the temperature, higher is the rate of evaporation and so on. Therefore, the highest rate of evaporation occurs in deserts in conditions Of great heat and lack of surface cone.
The surface of oceans is the greatest source of atmospheric moisture. Vegetation is an important factor, particularly in evapotranspiration. Because, under transpiration, the loss of water takes place from the green plants resulting in a stream of water with dissolved mineral salts surfing up through the plants.

Q15: Why dew is not formed on cloudy, windy nights and in shady places?
Ans: Dew is formed when objects radiate heat thoroughly so that the moist air coming into contact with them may be sufficiently cooled down and the water vapour condenses into water droplets. The clouds act as a blanket for the earth’s surface. They check the radiation of heat so it does not radiate heat thoroughly. Hence, dew is not formed on cloudy nights and in shady places.
Similarly, dew is not formed on windy nights, because the winds blow fast and the moist air does not come long enough into contact with cold objects to get cooled. Hence, condensation does not take place and no dew can be formed.

Q16: Write short notes on:
(i) Convectional precipitation
Ans: Convectional precipitation occurs when the sun's heat causes the Earth's surface to warm, leading to the air near the ground also becoming warm. Warm air is lighter and rises. As it ascends, it cools and condenses, forming clouds. When these clouds reach a certain saturation point, the water droplets combine and fall as rain. Convectional precipitation is common in tropical regions with high temperatures, often resulting in afternoon thunderstorms. It plays a vital role in the water cycle and is a primary source of water for agriculture in many parts of the world.

(ii) Cyclonic precipitation
Ans: Cyclonic precipitation, also known as frontal precipitation, occurs when warm and cold air masses meet. The warm air, being lighter, rises over the denser, cooler air. As the warm air rises, it cools, condenses, and forms clouds, leading to precipitation. Cyclonic precipitation is common in mid-latitude regions, where weather fronts frequently clash, causing rain or snow. These weather systems are responsible for extended periods of precipitation and are associated with various types of severe weather, including thunderstorms, hail, and blizzards.

(iii) Orographic precipitation
Ans: Orographic precipitation occurs when moist air is forced to rise over elevated landforms such as mountains. As the air ascends, it cools and condenses, forming clouds and leading to precipitation. The windward side of the mountain (the side facing the oncoming wind) experiences heavy rainfall, while the leeward side (rain shadow region) is relatively dry. Orographic precipitation is a significant factor in shaping landscapes and ecosystems. It creates lush, green environments on the windward sides of mountains and arid regions on the leeward sides, where the descending air warms and dries, leading to reduced precipitation.

Q17: Why does the amount of water vapour decrease rapidly with altitude?
Ans: The amount of water vapor in the atmosphere decreases rapidly with altitude due to decreasing atmospheric pressure and temperature with height. Here's how these factors contribute to the decrease in water vapor content:

• Decreasing Atmospheric Pressure: As you ascend in the atmosphere, the atmospheric pressure decreases. At higher altitudes, there are fewer air molecules per unit volume. Since water vapor is just one component of the air, a decrease in the number of air molecules also means a decrease in the number of water vapor molecules. The lower pressure at higher altitudes means there's less space for water vapor to exist in a gaseous state.
• Decreasing Temperature: Temperature generally decreases with altitude in the troposphere, the lowest layer of the Earth's atmosphere where weather occurs. As air rises, it expands and cools due to the decrease in pressure. Cooler air can hold less moisture than warm air because colder temperatures reduce the air's capacity to hold water vapor. This phenomenon is described by the concept of relative humidity, which is the ratio of the actual amount of water vapor in the air to the maximum amount of water vapor the air could hold at that temperature. When air rises and cools, it may reach its saturation point, leading to the condensation of water vapor into clouds and precipitation.

Due to the combined effects of decreasing atmospheric pressure and temperature with altitude, the amount of water vapor in the atmosphere diminishes rapidly as you go higher, eventually leading to the formation of clouds and precipitation, particularly in regions where air is forced to rise, such as along mountain slopes or in weather systems.