NCERT Solutions for Class 7 Geography Chapter 4 - Air

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Chapter 4 - Air Exercise 27

Solution 1

(i) Earth is enveloped by a blanket of air. This envelopment/blanket is called ‘atmosphere’.

(ii) Oxygen and nitrogen constitute the bulk of the atmosphere.

(iii) Carbon dioxide creates the greenhouse effect in the atmosphere.

(iv)Weather is the collection of short-term changes in the atmosphere of the Earth. It is, in essence, the hour-to-hour, day-to-day condition of the atmosphere.

(v) Convectional rainfall, orographic rainfall and cyclonic rainfall are the three types of rainfall.

(vi) Air pressure is the pressure exerted by the weight of the air on the surface of the Earth.

Solution 2

(i) – (c) Ozone

(ii) – (a) Troposphere

(iii) – (b) Stratosphere

(iv) – (b) Decreases

(v) – (b) Rain

Solution 3

(i) – (c) Permanent wind

(ii) – (d) Local wind

(iii) – (a) Seasonal wind

(iv) – (b) Horizontal movement of air

Solution 4

(i) Humidity is the amount of moisture or water vapour present in air at any particular point of time. On a humid day, the level of water vapour in the air is more and as the air gets warmer, this level too increases. As a result, wet clothes take longer time to dry on a humid day.

(ii) Insolation is in fact the incoming solar radiations that are intercepted by the Earth. There is a tilt in the axis of the Earth. As a result of this tilt, the sunlight, and by extension, the incoming radiations, cover a larger area at the Equator than at the Poles.