1. Multiple choice questions.
(i) Which one of the following is the most important constituent of the atmosphere for human beings?
(a) Water vapor (c) Dust particle (b) Nitrogen (d) Oxygen
(ii) Which one of the following process is responsible for transforming liquid into vapour?
(a) Condensation (b) Transpiration (c) Evaporation (d) Precipitation
(iii) The air that contains moisture to its full capacity :
(a) Relative humidity (b) Specific humidity (c) Absolute humidity (d) Saturated air
(iv) Which one of the following is the highest cloud in the sky?
(a) Cirrus (c) Nimbus (b) Stratus (d) Cumulus
2. Answer the following questions in about 30 words.
(i) Name the three types of precipitation.
Ans. Sleet, hailstorm and rain.
(ii) 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.
(iii) Why does the amount of water vapor decreases rapidly with altitude?
Ans. The transformation of water vapor into water is called condensation. Condensation is caused by loss of heat. Moist air rises and after reaching a level moist air cools. Because we know as we go up temperature drops. Now that moist air is cooled, water vapor condenses into liquid form. Water vapor are more active at low altitudes.
(iv) How are clouds formed? Classify them.
Ans. Water vapor in the atmosphere after condensation takes the form of 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.
Clouds are grouped under four types : (i) cirrus; (ii) cumulus; (iii) stratus; (iv) nimbus based on height, expanse, density and transparency or opaqueness.
3. Answer the following questions in about 150 words.
(i) Discuss the salient features of the world distribution of precipitation.
Ans. 1. Different places on the earth’s surface receive different amounts of rainfall in a year and that too in different seasons.
2. As we proceed from the equator towards the poles, rainfall goes on decreasing steadily.
3. Coastal areas of the world receive greater amounts of rainfall than the interior of landmass.
4. Rainfall occurs more over the oceans than on the landmasses.
5. Between 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.
6. Between 45 and 65 N and S of equator, due to the westerlies, the rainfall is first received on the western margins of the continents and it goes on decreasing towards the east.
7. Wherever mountains run parallel to the coast, the rain is greater on the coastal plain, on the windward side and it decreases towards the leeward side.
(ii) What are the forms of condensation? Describe the process of dew and frost formation.
Ans. Condensation is a phase where physical matter in the form of gas changes in to liquid. Different forms of condensation are:- dew, frost, fog and mist.
Dew formation:- 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. Ideal conditions are clear sky, calm air, high relative humidity, and cold and long nights.
Frost formation:- Frost forms on cold surfaces when condensation takes place below freezing point 0 degree Celsius which is below freezing point. Ideal temperature is same as dew but the air temperature must be below freezing point.