NCERT notes and solutions

Class 7

Geography

Chapter 4

AIR

Oxygen – The existence of life is due to the presence of oxygen

• The green plant takes outside oxygen during photosynthesis and takes in carbon-dioxide

Carbon-dioxide – It is ma major greenhouse gas

• It is useful for plants for preparing food.
• Plants take in Carbon dioxide which is released by Animals and humans.

Aur Circulation –  Air on heating expands up and becomes lighter. Cool air is heavy and goes down. The cool area fills the gap of the hot area.

Structure of the atmosphere –

5 layers of the atmosphere –

(i)Troposphere –

• height around 13 km
• Air present in this area
• Weather phenomenons like a waterfall, snowfall occur in this layer.

Tropopause – It is paint or line from where the stratosphere starts and the troposphere ends.

(ii) Stratosphere – 

• Range – 50km.
• Free from weather phenomenon.
• An airplane flies in this laya due to the absence of clouds.
• The ozone layer is present.

(iii) Mesosphere –

• Range – 80 km
• Meteorites burn up in this layer.

(iv)Thermosphere –  With an increase in height, the temperature rises in the thermosphere.

• Radio Communication.
• The ionization layer is present.
• It extends from 80 km- 400 km.

(v)Exosphere –

• Very thin air layer wake
• Light gases like Helium and Hydrogen floats into space from here.

Weather and climate – 

Weather –  It is the day-to-day condition of an atmosphere.

Climate –  Average weather condition of place over a long period of time.

Temperature –

• The degree of hotness and coldness of the air is temperature.
• An important factor that influences temperature is insolation that is solar energy that is trapped by the earth.
• The amount of insolation is more in the equator and goes on decreasing towards the pole.
• The standard unit of measuring temperature is degree celsius. Which was discovered by degree Anders celsius.

» Rain Gauge → Measure amount of rainfall.

» Thermometer → Measures temperature.

» The barometer→ Measures atmospheric pressure.

» Wind Vane→ Direction of the wind.

Exercise

1. Answer the following questions.

(i) What is the atmosphere?

Answer: It is a blanket of air that surrounds our earth. It protects us from harmful ultraviolet rays.

(ii) Which two gases make the bulk of the atmosphere?

Answer: Oxygen (21%)

Nitrogen (78%)

(iii) Which gas creates a greenhouse effect in the atmosphere?

Answer: Carbon dioxide gas creates a greenhouse effect in the atmosphere.

(iv) What is the weather?

Answer: It is the day-to-day condition of an atmosphere. 

(v) Name three types of rainfall?

Answer: 

1. Convectional rainfall
2. Orographic rainfall
3. Cyclonic rainfall

(vi) What is air pressure?

Answer: Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface. The air pressure decreases as height increases and is the highest at the sea level.

2. Tick the correct answer.

(i) Which of the following gases protects us from harmful sun rays?

(a) Carbon dioxide

(b) Nitrogen

(c) Ozone   

(ii) The most important layer of the atmosphere is

(a) Troposphere   

(b) Thermosphere

(c) Mesosphere

(iii) Which of the following layers of the atmosphere is free from clouds?

(a) Troposphere

(b) Stratosphere   

(c) Mesosphere

(iv) As we go up the layers of the atmosphere, the pressure

(a) Increases

(b) Decreases   

(c) Remains the same

(v) When precipitation comes down to the earth in the liquid form, it is called

(a) Cloud

(b) Rain   

(c) Snow

3. Match the following.

Answer:

4. Give reasons.

(i) Wet clothes take a longer time to dry on a humid day?

Answer: The amount of water in the air is high on humid days. Due to which the rate of evaporation decreases and the air absorb less water from the clothes.

(ii) Amount of insolation decreases from the equator towards poles?

Answer: The sun’s rays fall vertically at the equator and become oblique at the poles, which reduces the amount of disinfection from the equator toward the poles.