Textbook Solutions: The Atmosphere | Window on the Word Class 7: Solutions, Notes & Worksheets PDF Download

A. Choose the correct answer.

1.
Ans: (a)

2.
Ans: (d)

3.
Ans: (b)

4.
Ans: (b)

5.
Ans: (b)

Fill In the blanks

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

2.
Ans: Deforestation Increases the amount of carbon dioxide gases in the atmosphere.

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

4. 
Ans: Winds that blow in particular regions at particular times are called periodic winds.

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

C. Name the following.

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

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

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

4.
Ans: The heat zone between the Tropic of Capricorn and the Antarctic Circle: Temperate Zone

5.
Ans: A prevailing wind: Trade Wind

D. Answer in one or two sentences.

1.
Ans: The atmosphere is a thin layer of air that envelops the Earth, held to the surface by the planet's gravitational force, and plays a crucial role in sustaining life on Earth.

2.
Ans: The different layers of the atmosphere are the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere.

3.
Ans: Altitude affects atmospheric temperature as it decreases with an increase in altitude at an average rate of 1°C for every 165 m of ascent, because the air becomes thinner with a rise in altitude, so there are fewer particles to absorb heat.

4.
Ans: Air pressure is the pressure exerted by the weight of the air on the surface of the Earth, and it decreases with the increase in altitude.

5.
Ans: A cyclone is an intense tropical storm formed when the air over the sea heats up and rises, leading to the formation of an area of low pressure on the surface, characterized by heavy rainfall accompanied with strong, spiraling winds.

E. Answer in a paragraph.

1.
Ans: The atmosphere is a mixture of various gases such as nitrogen, oxygen, carbon dioxide, helium, ozone, argon, and hydrogen. Nitrogen, making up almost 78% of the atmosphere, is essential for the survival of plants. Oxygen, constituting about 21% of the air, is required by humans, plants, animals, and many other organisms for survival. Carbon dioxide, though making up just about 0.04% of the atmosphere, is one of the most important gases required by plants to perform photosynthesis. The atmosphere also contains aerosols, water vapor, and dust particles, contributing to its complex composition.

2.
Ans: Weather is the state of the atmosphere at a place over a short period of time, indicated by elements like temperature, moisture, precipitation, winds, and pressure. It changes from day to day, hour to hour, with changes occurring only in the troposphere. Climate, on the other hand, is the average atmospheric conditions of an area over a long period of time, arrived at after studying the variations in temperature, humidity, atmospheric pressure, wind, and precipitation. The main elements that influence weather and climate include temperature, pressure, winds, and precipitation.

3.
Ans: The Earth has several distinct heat belts due to the variations in the amount of insolation (incoming solar radiation) it receives. The Torrid Zone is the region between the equator and the Tropics of Cancer and Capricorn, and is the hottest of the three zones. The Temperate Zone lies between the Tropics and the Arctic and Antarctic Circles, with pleasant weather and temperatures neither as hot as the Torrid Zone nor as cold as the Frigid Zone. The Frigid Zone lies between the Arctic and Antarctic Circles and the North and South Poles, and is the coldest of the three regions.

4.
Ans: Pressure belts are broad belts or zones on the Earth's surface that experience similar pressure levels. They include the equatorial low pressure belt or the doldrums, the subtropical high pressure belts, the subpolar low pressure belts, and the polar high pressure belts. These pressure belts are permanent and determine the course of the wind.

5.
Ans: Wind is the movement of air from areas of high pressure to areas of low pressure. Permanent winds, also known as planetary or prevailing winds, blow from the same direction and follow the same course throughout the year. They move hot air from the equator towards the poles, and cold winds from the poles towards the equator, playing a vital role in maintaining global temperatures. The three types of permanent winds are Trade Winds, Westerlies, and Polar Easterlies.

6.
Ans: Periodic winds, like the monsoons, blow only during particular seasons and change their directions with the change in seasons. Examples of periodic winds include the south-west monsoon winds that blow from the sea to the land and bring rainfall during summers in India, and the north-east monsoon winds that blow in the opposite direction during winters.

7.
Ans: Humidity is the amount of water vapor or moisture in the atmosphere at any given point. Absolute humidity is the amount of water vapor present in unit volume of air, expressed in grams per cubic meter. Relative humidity is the ratio between the amount of moisture present in the air and the total amount of water vapor that the air can hold at that given temperature, expressed as a percentage.

8.
Ans: Rainfall can be of three types—convectional, relief, and cyclonic. Convectional rainfall is common near the equator and occurs when land gets heated up, causing the layer of air above it to rise, cool, and condense to form rain. Relief rainfall takes place when a mountain stands in the way of moisture-laden winds, causing the wind to rise, cool, and condense to bring rain. Cyclonic rainfall occurs when warm air is forced to rise by a body of cold air, leading to the formation of rain, and is associated with intense tropical storms called cyclones.