Q. 1. Name three sources of water-vapour.
Ans. Oceans, lakes, rivers.
Q. 2. Name the factors on which evaporation depends.
Ans. Aridity, temperature and movement of air.
Q. 3. What is condensation ?
Ans. Cooling of saturated air.
Q. 4. At what temperature, does condensation take place ?
Ans. At Dew Point.
Q. 5. What is the percentage of humidity at dew point ?
Ans. 100 per cent.
Q. 6. State the different forms of condensation.
Ans. Frost and snow, dew, fog, mist, clouds.
Q. 7. Name the instrument used for measuring humidity.
Q. 8. Name the two types of humidity.
Ans. Relative and Absolute humidity.
Q. 9. In which unit, is relative humidity measured ?
Ans. In percentages.
Q. 10. What is the relation between relative humidity and rainfall ?
Ans. When relative humidity is 100 per cent, rainfall takes place.
Q. 11. Name the different forms of precipitation.
Ans. Rain, snow, hailstone.
Q. 12. What is the general cause of rainfall ?
Ans. Cooling of saturated air.
Q. 13. Which instrument is used to measure rainfall ?
Q. 14. Name the type of daily rainfall in the equatorial region.
Ans. Convectional rainfall.
Q. 15. Name the dry area on the leeward slope of a mountain.
Q. 16. Name a rain-shadow area in India.
Ans. Deccan plateau.
Q. 17. Which region gets mostly rainfall in winter ?
Ans. Mediterranean Region.
Q. 18. Which type of rainfall occurs in N.W. India during winter ?
Ans. Cyclonic rainfall.
Q. 19. What do you mean by one centimetre of rainfall ?
Ans. Rainfall is measured in centimetre. One centimetre of rainfall means the amount of water that would cover a uniformly flat ground to the depth of one centimetre provided that none of water is evaporated; drained away or sinks into the ground.
Q. 20. What are clouds ?
Ans. Tiny droplets of water suspended in the air are known as clouds. These settle on the dust particles and float in the air as clouds. A cloud is a condensed moisture. It is formed by condensation of water vapour after dew point.
Q. 21. Describe the different types of clouds.
Ans. Clouds are classified into three groups according to their height :
(i) High Clouds: (Above 6 km.) Cirrus clouds are high clouds. It has a feathery appearance.
(ii) Medium Clouds: (2 km. to 6 km.) Cumulus clouds are medium clouds. These are wooly, and whitish clouds.
(iii) Low Clouds: Below 2 km Nimbus clouds are low clouds. These dark grey clouds give rain.
Q. 22. What is meant by the term ‘Humidity’ ?
Ans. Humidity means the amount of water vapour present in an air. Water-vapour is always present in an air. About 2% of the atmosphere consists of water vapour. Most of the water vapours of the atmosphere come from the oceans, lakes, rivers through evaporation.
Q. 23. Define Evaporation. Name the factors controlling the amount and rate of evaporation.
Ans. Evaporation: The process by which water is changed into water vapour (liquid to gaseous) is known as evaporation. The amount and rate of evaporation depend upon the following factors :
(i) Aridity. Dry air can absorb and retain more moisture than humid air.
(ii) Temperature. The higher the temperature, the higher is the rate of evaporation.
(iii) Movement of air. The greater the movement of the air, the greater is the evaporation.
(iv) Water bodies. Evaporation is greater on the oceans than on land.
Q. 24. What is dew point ? How is it related to the amount of moisture ?
Ans. Dew Point. The cooling of saturated air leads to condensation. The critical temperature at which the condensation of air begins is called Dew point. At dew point , an air is saturated to its maximum capacity. At dew point, the relative humidity is 100%.
Q. 25. How does condensation take place ? What are the different forms of condensation ?
Ans. Condensation. Condensation is the process by which water vapour of the atmosphere is changed to water (from gaseous to liquid state). Condensation starts when the temperature falls below dew point.
Forms of condensation. Condensation takes place in different forms such as :
(i) frost and snow.
(ii) dew, fog, mist, smog.
(iii) clouds, haze.
Q. 26. Define precipitation. Name its different forms.
Ans. Precipitation. Precipitation means ‘throwing down of moisture’ from atmosphere. It is the collective name given to different forms of moisture falling on the earth. Precipitation can be liquid or solid. It occurs in the following forms :
(i) Rainfall (ii) Snow (iii) Hail (iv) Sleet (v) Dew (vi) Frost (vii) Rime.
Q. 27. What is the relation between relative humidity and rainfall ?
Ans. As the relative humidity increases, the air becomes saturated. The relative humidity of the saturated air is 100 per cent. At this stage, air cannot hold any additional amount of moisture. Water vapour is condensed into water. The possibility of rain depends upon a high relative humidity.
Q. 28. What do you mean by the term ‘Smog’ ?
Ans. Smog is a combination of two words (smoke + fog). Very thick smoky fog is called smog. It is formed in industrial areas like Black country of Britain. It reduces the visibility to 200 metres.
Q. 29. What is Haze ? How is it caused ?
Ans. Haze is caused by smoke and dust particles in individual areas. It is caused to unequal refraction of light in air of different densities. It is caused in areas of low humidity. It reduces the visibility to 2 kms.
Q. 30. What is rain shadow ? Name one part of the Indian sub-continent that experiences rain shadow.
Ans. The leeward slope where the air descends and is dry is called rain shadow. Descending winds become warm and dry. There is no condensation. Deccan plateau lies in the rain shadow of Western Ghats.
Q. 31. Why does the equatorial region get daily rainfall in the afternoon ?
Ans. Sun’s rays fall vertical on the equator throughout the year. The land is intensely heated. The air expands, becomes lighter, and rises as convection currents. The rising air leads to cooling and condensation. Thus, torrential rainfall occurs daily in the afternoon.
Q. 32. How is rainfall caused ?
Ans. Rainfall. Humidity is the basis of rain. The general cause of rainfall is the cooling of the saturated air. The mechanism of rainfall passes through many stages.
(i) Condensation. The moist rising air is cooled, saturated and condensation takes place. (ii) Formation of clouds. Water vapour is condensed on the large number of dust particles to form clouds.
(iii) Formation of rain drops. The cloud droplets coalesce (merge) to form rain drops. One rain drop often contains one million cloud droplets. When these rain drops become so heavy that air cannot hold these, these fall on the earth in the form of rainfall. Thus, the release of moisture in the form of drops of water is called rainfall.
Q. 33. How is rainfall shown on maps ?
Ans. Rainfall is shown by isohytes on maps.
Isohytes are lines joining the places of equal amount of rainfall for a certain period. These lines are drawn by joining the places of equal rainfall.
Q. 34. Discuss the processes of adiabatic heating and cooling.
Ans . Adiabatic heating: When air moves downward or descends along a leeward slope, it is compressed. Compression results in heating of the air.
It is known as adiabatic heating.
Adiabatic cooling: When the air moves upward it expands. Expansion results in cooling of the air. It occurs in ascending winds or convection currents. It is known as adiabatic cooling. It is the process by which the temperature of air is reduced below the dew point.
This adiabatic cooling is responsible for formation of clouds and precipitation.
Q. 35. Discuss the factors which control the distribution of rainfall.
Ans. The distribution of the rainfall in the world depends on the following factors :
(i) Latitude. The amount of rainfall decreases from the equator towards the poles.
(ii) Distance from sea. Coastal areas get more rainfall than interiors of the continents.
(iii) Prevailing winds. Winds from sea bring rain, while winds from land are dry. Trade winds bring rain to the eastern parts, while the westerlies bring rain to the western parts.
(iv) Ocean currents. Winds blowing over warm ocean currents give rainfall over coastal areas. Cold currents increase the aridity of the coastal areas.
(v) Altitude. Mountains force winds to rise and are areas of high rainfall.
(vi) Direction of Mountains. Mountains like Aravalis lying parallel to the direction of winds are unable to check the winds and do not help in getting rainfall.
Q. 36. Write a note on Potential Evapotranspiration.
Ans. Potential Evapo-transpiration Evapo-transpiration is the amount of moisture transferred to the atmosphere by evaporation of liquid and solid water plus transpiration from living tissues principally from plants. The term ‘potential evapotranspiration’ refers to idealised conditions in which there would be enough rainfall to provide sufficient moisture for all possible evapo-transpiration in an area. In order to determine the potential evapotranspiration for any place or area, several factors like temperature, latitude, vegetation, permeability and water retention capacity of the soil are taken into consideration. Places having surplus precipitation over evapo-transpiration marked by surplus of under ground water storage.