Chapter - 4 The Atmosphere Exercise Answers

Exercise Answers

A. Choose the correct answer.

1. The atmosphere is held to the surface of the earth by:

a. The gravitational pull of the earth
b. The gravitational pull of the Sun
c. The rotation of the earth
d. Greenhouse gases

Ans. a. The gravitational pull of the earth

2. This gas makes up the bulk of the atmosphere:

a. Oxygen
b. Carbon dioxide
c. Hydrogen
d. Nitrogen

Ans. d. Nitrogen

3. All the weather phenomena like rainfall, storm, fog occur in this layer of the atmosphere:

a. Stratosphere
b. Troposphere
c. Ionosphere
d. Thermosphere

Ans. b. Troposphere

4. This layer helps in wireless communication and radio transmission:

a. Exosphere
b. Ionosphere
c. Mesosphere
d. Troposphere

Ans. b. Ionosphere

5. Rainfall caused when moist air comes in contact with the mountain is called:

a. Convectional rainfall
b. Relief rainfall
c. Cyclonic rainfall
d. Planetary rainfall

Ans. b. Relief rainfall

B. Fill in the blanks.

1. Oxygen constitutes _________ % of the atmosphere. 
Ans. 21

2. Deforestation increases the amount of __________ gases in the atmosphere. 
Ans. greenhouse

3. The decrease in temperature by 1° every 165 m of ascent in the troposphere is called the ________ rate. 
Ans. normal lapse

4. Winds that blow in particular regions of at particular times are called ________ winds. 
Ans. Local

5. The total amount of water vapour in a given volume of air is called ________. 
Ans. humidity

C. Name the following.

1. A by-product of photosynthesis: ________
Ans. Oxygen

2. The layer in which meteorites burn up: ________
Ans. Mesosphere

3. The average atmospheric condition of a place over a long period of time: ________
Ans. Climate

4. The heat zone between the tropic of Capricorn and the Antarctic circle: _________
Ans. Temperate zone

5. A prevailing wind: _________
Ans. Planetary wind

D. Answer in one or two sentences.

1. What is the atmosphere?

Ans. The earth is surrounded by a blanket of air called the atmosphere. The atmosphere is held down to the surface by the earth's gravitational force. 

2. Name the different layers of the atmosphere. 

Ans. The different layers of the atmosphere are:
a. The troposphere
b. The stratosphere
c. The mesosphere
d. The thermosphere and 
e. The exosphere

3. How does altitude affect atmospheric temperature?

Ans. Atmospheric temperature decreases with an increase in altitude at an average rate of 1 degree Celsius for every 165 m of ascent.

4. What is air pressure?

Ans. Air pressure is the force exerted by the weight of the air on Earth. Pressure decreases with an increase in height or temperature. 

5. What is a cyclone?

Ans. In the tropical areas, cyclonic rainfall is associated with intense tropical storms called cyclones.