NCERT Solutions for Class 11 Geography Chapter 10 - Water in the Atmosphere

70. Multiple choice questions.

(i) Which one of the following is the most important constituent of the atmosphere for human beings?

(a) Water vapour

(b) Nitrogen

(c) Dust particle

(d) Oxygen

Ans. (d) Oxygen

(ii) Which one of the following process is responsible for transforming liquid into vapour?

(a) Condensation

(b) Transpiration

(c) Evaporation

(d) Precipitation

Ans. (c) Evaporation

(iii) The air that contains moisture to its full capacity:

(a) Relative humidity

(b) Specific humidity

(c) Absolute humidity

(d) Saturated air

Ans. (d) Saturated air.

(iv) Which one of the following is the highest cloud in the sky?

(a) Cirrus

(b) Stratus

(c) Nimbus

(d) Cumulus

Ans. (a) Cirrus

71. Answer the following questions in about 30 words.

(i) Name the three types of precipitation.

Ans. There are many forms of precipitation like dew, fog, rainfall, snowfall, hailstones etc.

(a) Rainfall: The precipitation in the form of water is called rainfall.

(b) Snowfall: When the temperature is lower than 0°C, precipitation is called snowfall in the form of fine snowflakes.

(c) 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.

(ii) Explain relative humidity.

Ans. Relative humidity is the ratio of the amount of moisture in the air to its  maximum capacity at a certain temperature. Overseas, it is highest, while over continents, it is lowest. The ability to hold moisture increases or decreases as the air temperature changes and the relative humidity is also impacted.

(iii) Why does the amount of water vapour decreases rapidly with altitude?

Ans. The amount of water vapour in the air is influenced by the rate of evaporation and the air’s temperature, which dictates how much water vapour it can contain. With height, temperature and evaporation both fall, and as a result, water vapour also falls rapidly.

(iv) How are clouds formed? Classify them.

Ans. Cloud is a mass of minute water droplets or tiny ice crystals 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:

(a) cirrus

(b) cumulus

(c) stratus

(d) nimbus

72. Answer the following questions in about 150 words.

(i) Discuss the salient features of the world distribution of precipitation.

Ans. Salient features of the world distribution of precipitation are given below:

(a) Varied areas on the surface of the earth experience different annual rainfall totals, as well as seasonal variations. In general, rainfall continues to decline progressively as we move further from the equator and toward the poles. The world’s coastal regions experience more rainfall than the interiors of the continents.

(b) Between latitudes 35 and 40 degrees N and S of the equator, rain falls more frequently on the eastern shores and goes on decreasing towards the west. However, the more rainfall begins to fall on the western boundaries of the continents between 45 and 65 degrees N and S of the equator and then gradually decreases toward the east.

(c) The primary precipitation regimes of the world are classified as follows based on the total yearly precipitation:

  1. Over 200 cm of rainfall annually falls in the equatorial belt, the windward slopes of the mountains along the western shores of the cold temperate zone, and the coastal regions of the monsoon country.
  2. The annual rainfall in interior continental zones ranges from 100 to 200 cm.
  3. The continents’ coastal regions experience average rainfall.
  4. Rainfall in the temperate countries’ eastern and inner regions, the centre portions of tropical lands ranges from 50 to 100 cm annually.

(ii) What are forms of condensation? Describe the process of dew and frost formation.

Ans. The transformation of water vapour into water is called condensation. The loss of heat causes condensation. 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 occurs when the temperature of the air is reduced to dew point with its volume remaining constant.

(a) Dew: It is the term for moisture deposited as water droplets on cooled solid objects, such as rocks, grass blades, and plant leaves, as opposed to air nuclei above the surface.

(b) Frost: It is produced when condensation occurs on cold surfaces below the freezing point (0°C), i.e., when the dew point is equal to or lower than the freezing point.

(c) Fog and Mist: When the temperature of an air mass containing a significant amount of water vapour suddenly drops, condensation occurs on tiny dust particles inside the air mass. In other words, the fog is a cloud whose base is at or extremely close to the ground.

(d) Smog: This situation is referred to as smog when smoke and fog are present.

(e) 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.

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