Q 1 – Name the three types of precipitation.
Ans. There are many forms of precipitation like dew, fog, rainfall, snowfall, hailstones etc.
- Rainfall: The precipitation in the form of water is called rainfall.
- Snowfall: When the temperature is lower than the 0°C, precipitation takes place in the form of fine flakes of snow and is called snowfall.
- Hailstones: Sometimes, drops of rain after being released by the clouds become solidified into small rounded solid pieces of ice and which reach the surface of the earth are called hailstones.
Q 2 – Explain relative humidity.
Ans. The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity. It is highest over oceans and lowest over continents. With the change of air temperature, the capacity to retain moisture increases or decreases and the relative humidity is also affected.
The quantity of water vapour existing in the air depends upon the rate of evaporation and the temperature of the air which determines its holding capacity of water vapour. Both temperature and evaporation decreases with altitude and as a result water vapour also decreases rapidly with altitude.
Q 3 – How are clouds formed? Classify them.
Ans. Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water vapour in free air at considerable elevations. As the clouds are formed at some height over the surface of the earth, they take various shapes. According to their height, expanse, density and transparency or opaqueness clouds are grouped under four types :
- cirrus
- cumulus
- stratus
- nimbus.
Q 4 – Discuss the salient features of the world distribution of precipitation.
Ans. Salient features of the world distribution of precipitation are given below:
1. Different places on the earth’s surface receive different amounts of rainfall in a year and that too in different seasons. In general, as we proceed from the equator towards the poles, rainfall goes on decreasing steadily. The coastal areas of the world receive greater amounts of rainfall than the interior of the continents. The rainfall is more over the oceans than on the landmasses of the world.
2. Between the latitudes 35° and 40° N and S of the equator, the rain is heavier on the eastern coasts and goes on decreasing towards the west. But, between 45° and 65° N and S of equator, the rainfall is first received on the western margins of the continents and it goes on decreasing towards the east.
3. In some regions rainfall is distributed evenly throughout the year such as in the equatorial belt and in the western parts of cool temperate regions. .
4. On the basis of the total amount of annual precipitation, major precipitation regimes of the world are identified as follows
- The equatorial belt, the windward slopes of the mountains along the western coasts in the cool temperate zone and the coastal areas of the monsoon land receive heavy rainfall of over 200 cm per annum.
- Interior continental areas receive moderate rainfall varying from 100-200 cm per annum.
- The coastal areas of the continents receive moderate amount of rainfall.
- The central parts of the tropical land and the eastern and interior parts of the temperate lands receive rainfall varying between 50-100 cm per annum.
- Areas lying in the rain shadow zone of the interior of the continents and high latitudes receive very low rainfall-less than 50 cm per annum.
Q 5 – What are forms of condensation? Describe the process of dew and frost formation.
Ans. Condensation: The transformation of water vapour into water is called condensation. Condensation is caused by the loss of heat. When the water vapour or the moisture in the atmosphere takes one of the following forms — dew, frost, fog and clouds. Forms of condensation can be classified on the basis of temperature and location. Condensation takes place when the dew point is lower than the freezing point as well as higher than the freezing point.
- Dew: When the moisture is deposited in the form of water droplets on cooler surfaces of solid objects (rather than nuclei in air above the surface) such as stones, grass blades and plant leaves, it is known as dew.
- Frost: Frost forms on cold surfaces when condensation takes place below freezing point (CPC), i.e. the dew point is at or below the freezing point.
- Fog and Mist: When the temperature of an air mass containing a large quantity of water vapour falls all of a sudden, condensation takes place within itself on fine dust particles. So, the fog is a cloud with its base at or very near to the ground.
- Smog: Such a condition when fog is mixed with smoke, is described as smog.
- Clouds: Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water vapour in free air at considerable elevations. As the clouds are formed at some height over the surface of the earth, they take various shapes.
Q 6 – What is smog?
Ans. Such a condition when fog is mixed with smoke, is described as smog.
Q 7 – How is humidity received in atmosphere?
Ans. The moisture in the atmosphere is derived from water bodies through evaporation and from plants through transpiration.
Q 8 – What is relative humidity?
Ans. The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.
Q 9 – What is absolute humidity?
Ans. The actual amount of the water vapour present in the atmosphere is known as the absolute humidity. It is the weight of water vapour per unit volume of air and is expressed in terms of grams per cubic metre.
Q 10 – By what processes there a continuous exchange of water between the atmosphere, the oceans and the continents?
Ans. There is a continuous exchange of water between the atmosphere, the oceans and the continents through the processes of evaporation, transpiration, condensation and precipitation.
Q 11 – How are clouds classified?
Ans. According to their height, expanse, density and transparency or opaqueness clouds are grouped under four types :
- cirrus;
- cumulus;
- stratus;
- nimbus
A combination of these four basic types can give rise to the following types of clouds: high clouds cirrus, cirrostratus, cirrocumulus; middle clouds—altostratus and altocumulus; low clouds—stratocumulus and nimbostratus and clouds with extensive vertical development cumulus and cumulonimbus.’’
Q 12 – When does condensation take place?
Ans. The transformation of water vapour into water is called condensation. Condensation is caused by the loss of heat.
Q 13 – What are the suitable conditions for making of dew?
Ans. The ideal conditions for its formation are clear sky, calm air, high relative humidity, and cold and long nights. For the formation of dew, it is necessary that the dew point is above the freezing point.
Q 14 – What are hailstones?
Ans. Sometimes, drops of rain after being released by the clouds become solidified into small rounded solid pieces of ice and which reach the surface of the earth are called hailstones.
Q 15 – What is rain shadow area?
Ans. The area situated on the leeward side, which gets less rainfall is known as the rain-shadow area.
Q 16 – What is precipitation?
Ans. After the condensation of water vapour, the release of moisture is known as precipitation. This may take place in liquid or solid form.
Q 17 – What is convectional rain?
Ans. Convectional Rain: The air on being heated, becomes light and rises up in convection currents. As it rises, it expands and loses heat and consequently, condensation takes place and cumulous clouds are formed. With thunder and lightening, heavy rainfall takes place but this does not last for long
Q 18 – What factors influence the process of condensation?
Ans. Condensation is influenced by the volume of air, temperature, pressure and humidity. Condensation takes place:
- when the temperature of the air is reduced to dew point with its volume remaining constant;
- when both the volume and the temperature are reduced;
- when moisture is added to the air through evaporation.
Q 19 – Name and define three important types of rainfall.
Ans. On the basis of origin, rainfall may be classified into three main types:
- The convectional rain
- Orographic or relief rain and
- Cyclonic or frontal rainfall
1. Convectional rain: The air on being heated, becomes light and rises up in convection currents. As it rises, it expands and loses heat and consequently, condensation takes place and cumulous clouds are formed. With thunder and lightening, heavy rainfall takes place but this does not last for long.
Such rain is common in the summer or in the hotter part of the day. It is very common in the equatorial regions and interior parts of the continents, particularly in the northern hemisphere.
2. Orographic rain: When the saturated air mass comes across a mountain, it is forced to ascend and as it rises, it expands; the temperature falls, and the moisture is condensed. In this sort of rain the windward slopes receive greater rainfall. After giving rain on the windward side, when these winds reach the other slope, they descend, and their temperature rises. Then their capacity to take in moisture increases and hence, these leeward slopes remain rainless and dry. The area situated on the leeward side, which gets less rainfall is known as the rain-shadow area. It is also known as the relief rain.
3. Cyclonic rainfall: These rains take place in low pressure areas where air moves from low pressure area to high pressure are a and this movement brings rainfall.
Q 20 – Explain the process of evaporation.
Ans. Evaporation is a process by which water is transformed from liquid to gaseous state. Heat is the main cause for evaporation. The temperature at which the water starts evaporating is referred to as the latent heat of vapourisation. Increase in temperature increases water absorption and retention capacity of the given parcel of air. Similarly, if the moisture content is low, air has a potentiality of absorbing and retaining moisture. Movement of air replaces the saturated layer with the unsaturated layer. Hence, the greater the movement of air, the greater is the evaporation.
Q 21 – Explain cyclonic rain.
Ans. Air expands when heated and gets compressed when cooled. This results in variations in the atmospheric pressure. The result is that it causes the movement of air from high pressure to low pressure, setting the air in motion. Air in horizontal motion is wind. Atmospheric pressure also determines when the air will rise or sink. The wind redistributes the heat and moisture across the planet, thereby, maintaining a constant temperature for the planet as a whole. The vertical rising of moist air cools it down to form the clouds and bring precipitation. It is called cyclonic rain.
Q 22 – Explain about condensation in detail.
Ans.
1. Meaning: The transformation of water vapour into water is called condensation. Cause: Condensation is caused by the loss of heat.
2. Sublimation: When moist air is cooled, it may reach a level when its capacity to hold water vapour ceases. Then, the excess water vapour condenses into liquid form. If it directly condenses into solid form, it is known as sublimation.
3. Process: In free air, condensation results from cooling around very small particles termed as hygroscopic condensation nuclei. Particles of dust, smoke and salt from the ocean are particularly good nuclei because they absorb water. Condensation also takes place when the moist air comes in contact with some colder object and it may also take place when the temperature is close to the dew point. Condensation, therefore, depends upon the amount of cooling and the relative humidity of the air.
Factors affecting condensation:
- When the temperature of the air is reduced to dew point with its volume remaining constant;
- When both the volume and the temperature are reduced;
- When moisture is added to the air through evaporation.
However, the most favourable condition for condensation is the decrease in air temperature. After condensation the water vapour or the moisture in the atmosphere takes form of dew, frost, fog and clouds.
Q 23 – Explain about fog and mist.
Ans. When the temperature of an air mass containing a large quantity of water vapour falls all of a sudden, condensation takes place within itself on fine dust particles. So, the fog is a cloud with its base at or very near to the ground.
- Because of the fog and mist, the visibility becomes poor to zero. In urban and industrial centres smoke provides plenty of nuclei which help in the formation of fog and mist.
- Such a condition when fog is mixed with smoke, is described as smog.
- The only difference between the mist and fog is that mist contains more moisture than the fog.
- In mist each nuceli contains a thicker layer of moisture. Mists are frequent over mountains as the warm air rises up the slopes and meets a cold surface.
- Fogs are drier than mist and they are prevalent where warm currents of air come in contact with cold currents. Fogs are mini clouds in which condensation takes place around nuclei provided by the dust, smoke, and the salt particles.
Q 24 – On the basis of rainfall received, in how many groups can we classify the world?
Ans. On the basis of rainfall received, we can classify the world into five groups.
- The equatorial belt, the windward slopes of the mountains along the western coasts in the cool temperate zone and the coastal areas of the monsoon land receive heavy rainfall of over 200 cm per annum.
- Interior continental areas receive moderate rainfall varying from 100 – 200 cm per annum.
- The coastal areas of the continents receive moderate amount of rainfall.
- The central parts of the tropical land and the eastern and interior parts of the temperate lands receive rainfall varying between 50-100 cm per annum.
- Areas lying in the rain shadow zone of the interior of the continents and high latitudes receive very low rainfall-less than 50 cm per annum
Q 25 – Use a diagram to explain the process of evaporation.
Ans. Evaporation is a process by which water is transformed from liquid to gaseous state. Heat is the main cause for evaporation. Movement of air replaces the saturated layer with the unsaturated layer. Hence, the greater the movement of air, the greater is the evaporation.
Q 26 – What is the greatest source of atmospheric moisture?
Ans. The surface of the ocean is the greatest source of atmospheric moisture.
Q 27 – What is meant by humidity?
Ans. The state of the atmosphere with respect to its content of moisture or water vapour is called humidity.
Q 28 – What is meant by sensible temperature?
Ans. It is the cold or heat felt by the human body, depending not only on actual temperature but also on relative humidity and wind.
Q 29 – Name three states in which water exists.
Ans. Water exists in three states or forms:
- Solid (ice),
- Liquid (water),
- Gas (water vapour).
Q 30 – What is the greatest source of atmospheric moisture?
Ans. The surface of the ocean is the greatest source of atmospheric moisture.
Q 31 – What is meant by humidity?
Ans. The state of the atmosphere with respect to its content of moisture or water vapour is called humidity.
Q 32 – What is meant by sensible temperature?
Ans. It is the cold or heat felt by the human body, depending not only on actual temperature but also on relative humidity and wind.
Q 33 – 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.
Q 34 – What is the measure of absolute humidity?
Ans. Absolute humidity is measured in grams per cubic metre (g/m3).
Q 35 – 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.
Q 36 – Why dew and frost form on grass quite readily?
Ans. Because grass is a good radiator and, therefore, cools quickly.
Q 37 – Identify various forms of precipitation.
Ans. Various forms of precipitation include rainfall, snowfall, hail, sleet and drizzle.
Q 38 – Name three types of precipitation.
Ans. The three types of precipitation are convectional, orographic and cyclonic precipitation.
Q 39 – 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.
Q 40 – What is the source of atmospheric moisture?
Ans. The oceanic surface is the main source of atmospheric moisture.
Q 41 – Which factors control evaporation?
Ans. There are three main factors which control evaporation:
- aridity,
- temperature,
- movement of air.
Q 42 – Name the various types of clouds.
Ans. Cirrus clouds, stratus clouds, stratocumulus and cumulus clouds.
Q 43 – What are the different types of fog?
Ans. Fogs are of three types: radiating, advection and frontal fog.
Q 44 – What is condensation?
Ans. Cooling of saturated air is called condensation.
Q 45 – What are the different types of rainfall?
Ans. Rainfall is of three types: convectional, orographic and cyclonic rainf
Q 46 – What is sublimation?
Ans. The process of conversion of ice into liquid or vapour is known as sublimation.
Q 47 – Name the temperature at which a given sample of air becomes saturated.
Ans. Dew point.
Q 48 – What do you mean by saturated air?
Ans. The air that contains moisture to full capacity.
Q 49 – What is relative humidity?
Ans. The ratio of the amount of water vapour actually presents in the air at a particular temperature to the amount of water vapour required to saturate the same air at the same temperature.
Q 50 – What is sleet?
Ans. The falling of frozen raindrops and frozen melted snow on the earth’s surface is known as sleet.
Q 51 – Name the various types of humidity.
Ans. Absolute humidity, specific humidity and relative humidity.
Q 52 – 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 53 – 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 54 – 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 56 – 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
- Clouds which slow down terrestrial radiation.
Q 57 – 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.
Q 58 – Why does the amount of water vapour decrease rapidly with altitude?
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 59 – 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 60 – 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.
- There should be dust particles in the air.
Q 61 – 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.
Q 62 – Why does the amount of water vapour decrease rapidly with altitude?
Ans. The amount of water in the atmosphere is variable from place to place and from time to time. It decreases rapidly with altitude. The temperature decreases as the altitude increases.
Q 63 – 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.
Q 64 – Describe the conditions for the formation of dew.
Ans. Following are the favourable conditions for the formation of dew:
- Clear sky
- Calmness, i.e., the wind should not blow
- High relative humidity
- Rich vegetation cover
- Long nights
Q 65 – 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.
Q 66 – Describe the various forms of precipitation and the major precipitation regimes of the world.
Ans. Precipitation results from the continued condensation and growth of the moisture particles until they become too large to remain suspended in the air.
If condensation takes place at a temperature above 0°C, the resulting precipitation is in the form of rain.
If the process through a layer of colder air on the way down, it may freeze and fall as sleet.
In a strong turbulent current of a thunderstorm, water drops may be carried upward into freezing temperatures and eventually fall as hail. In fact, violent air currents may keep hailstones shuttling up and down until they grow to enormous sizes.