Q 2 – What is the energy required to change water’s state or phase, without changing its temperature called? (a) Latent heat of the Earth (b) Latent heat of the water (c) Latent heat of the rock (d) Latent heat of the atmosphere
Q 3 – When air containing water reaches its saturation point, then (a) No more water evaporates from the ground (b) It leads to evaporation above sea and precipitation above land. (c) Water vapour forms droplets (d) The droplets fall out of the clouds
Q 4 – The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the (a) Relative humidity (b) Specific humidity (c) Absolute humidity (d) Saturated air
Q 6 – The actual amount of the water vapour present in the atmosphere is known as _________ (a) Relative humidity (b) Absolute humidity (c) Condensation (d) None of the above
Q 8 – When the water containing air becomes saturated, then (a) it will be calm (b) it will be windy above sea and rainy above land (c) it will start to rain (d) clouds will be formed
Q 10 – The air can only contain a certain amount of water vapour before it is saturated. This amount is dependent on (a) the temperature of the air (b) whether the air is above sea or land (c) the wind speed (d) the amount of dust particles in the air
Ans. Water exists in three forms, solid (ice), liquid (water) and gas-(vapour). All three states are interchangeable. The change of solid to ‘ liquid is called melting; from liquid to solid is freezing; from liquid to gas is evaporation and from gas to liquid is condensation. But sometimes ice directly converts into vapour or vice-versa. This is called sublimation.
Q 18 – Describe various processes involved in the change of state (form) of water.
Ans. Water exists in three forms, solid (ice), liquid (water) and gas-(vapour). All three states are interchangeable. The change of solid to ‘ liquid is called melting; from liquid to solid is freezing; from liquid to gas is evaporation and from gas to liquid is condensation. But sometimes ice directly converts into vapour or vice-versa. This is called sublimation.
Q 19 – Describe various sources of atmospheric moisture on the earth.
Ans. The surface of the ocean is the greatest source of atmospheric moisture. Besides, smaller water bodies, vegetation and damp surfaces also contribute significant amounts of moisture.
Q 20 – 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.
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Q 21 – 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.
Q 22 – Discuss the reasons which impede the formation of dew or frost.
Ans. On cool nights in early winter, when Radiation from the ground is relatively rapid, the air in contact with the ground may be chilled to the dew point and moisture condenses on the leaves and grass in the form of dew. If the dew point is below the freezing point, the condensation takes place in the form of ice crystals or frost. The formation of dew or frost is impeded by
Dry air,
Wind mixes the air and prevents its lower portion from reaching the dew point, and
Ans. Water vapour in the atmosphere is the result of the evaporation of water from the earth’s surface, a continual process dependent on air. Since the air becomes thinner with the altitude, so also does the water vapour.
Q 25 – 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.
Q 26 – What is precipitation? What are the conditions to determine the form of precipitation?
Ans. Precipitation is a process of condensation of water vapour in ‘ the atmosphere which falls to the earth in the form of rain, snow, hail or sleet. These are the various forms of precipitation. Conditions for precipitation.
There should be evaporation so that the relative humidity is „ high in the air.
There should be adiabatic cooling of the moist air.
1. Relative humidity and Absolute humidity: Relative humidity:
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.
Absolute humidity: It is the actual amount of water vapour present per unit volume of air and it is measured in grams per cubic meter.
2. Evaporation and Condensation Evaporation is the process by which a solid or liquid is converted to a gaseous state or 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.
Condensation: 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.
3. Dew and Frost: Dew: When the moisture is deposited in the form of water droplets on cooler surfaces of solid objects, such as stones, grass blades and plant leaves, it is known as dew. Clear sky, calm air, high relative humidity, cold and long nights are the ideal conditions for the formation of dew.
Frost: Frost forms on cold surfaces at a dew point which is at or below the freezing point when an excess of moisture is deposited in the form of minute ice crystals instead of droplets of water.
Write short notes on: (a) Convectional precipitation (b) Cyclonic precipitation (c) Orographic precipitation
(a) Convectional precipitation: It occurs when moist air over the heated ground becomes warmer than the surrounding air and is forced to rise, expand, cool and yield some of its moisture.
Convectional rain is common in low latitudes and usually comes in the form of short heavy showers, often during the hottest part of the day. Thunder and lightning generally accompany the showers. If the convection currents are especially strong and turbulent, hail is formed.
(b) Cyclonic precipitation: It occurs in low-pressure areas, where cyclonic winds coming from various directions converge and force the large volumes of light air to rise and cause rain.
Cyclonic precipitation is generally associated with the passage of depression in middle or high latitudes, as the warm moist air mass of the depression rises and over-rides colder, heavier air.
(c) Orographic precipitation: It is caused due to relief. It occurs when the moist wind is forced to rise over a mountain or any other height. Precipitation occurs due to cooling of moisture-laden air as it rises over a high relief barrier. It happens, particularly on the windward slopes! On the other side of the barrier or on the leeward side of the slopes, there develops rain shadow area with no or very little rainfall because as the moisture-laden wind descends down the slope, after precipitating on the windward side, it becomes warmer and drier. Such a situation occurs along the western coasts of Qudra, North America and South America. The moist air from the Arabian Sea is forced by Sahyadri hills of the Western Ghats to rise up resulting in expansion, cooling and rainfall.
Amount of precipitation depends on slope, the height of the hills, temperature and moisture content of the air mass. On the other side of the mountain, the descending wind is devoid of moisture and, hence, does not give rain. The eastern slope of Sahyadri mountains in India falls in the rain shadow area.
Q 30 – 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.
