Test: Air - Class 7 MCQ

Answer: C) Atmosphere

Topic in NCERT: ATMOSPHERE

Line in NCERT: "Our earth is surrounded by a huge blanket of air called atmosphere. All living beings on this earth depend on the atmosphere for their survival. It provides us the air we breathe and protects us from the harmful effects of the sun's rays."

The stratosphere is indeed almost free from clouds and is considered ideal for flying aeroplanes. This layer also contains a protective layer of ozone gas, which shields us from harmful sun rays. This absence of clouds and associated weather phenomena makes it safer for aircraft to travel without encountering turbulent weather conditions.

Topic in NCERT: STRATOSPHERE

Line in NCERT: "This layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aeroplanes."

Air pressure is highest at sea level because the column of air above us is tallest, thus exerting the maximum pressure. As we ascend in altitude, the height of the air column decreases, resulting in a reduction in air pressure. Therefore, as we move away from sea level and ascend to higher elevations, the air pressure progressively diminishes. This principle explains why air pressure is greatest at sea level and decreases with increasing altitude.

Topic in NCERT: Air Pressure

Line in NCERT: "The air pressure is highest at sea level and decreases with height."

The correct answer is C: Ionosphere.

• The ionosphere is a layer of Earth's atmosphere that contains a high concentration of ions and free electrons.
• This layer extends from about 50 km to 1,000 km above the Earth's surface.
• It plays a crucial role in radio communication by reflecting certain frequencies of radio waves back to Earth.
• By reflecting radio waves, the ionosphere helps in long-distance radio transmission, allowing signals to travel beyond the horizon.

Topic in NCERT: THERMOSPHERE

Line in NCERT: "Ionosphere is a part of this layer. It extends between 80-400 km. This layer helps in radio transmission. In fact, radio waves transmitted from the earth are reflected back to the earth by this layer."

Weather refers to the short-term conditions of the atmosphere at a specific time and place. It includes factors such as temperature, humidity, wind speed, precipitation (rain, snow, etc.), and atmospheric pressure. Weather can change rapidly over minutes, hours, or days.

For example, weather describes if it is sunny, cloudy, raining, or snowing today. It focuses on immediate, day-to-day atmospheric conditions.

In contrast:

• Climate refers to the long-term average of weather patterns over a period of time (usually 30 years or more) in a specific region.
• Humidity is the amount of moisture or water vapor in the air.
• Precipitation refers to any form of water that falls from clouds, such as rain, snow, sleet, or hail.

Thus, weather is the correct term for the short-term state of the atmosphere.

Topic in NCERT: WEATHER AND CLIMATE

Line in NCERT: "Weather is this hour-to-hour, day to day condition of the atmosphere."

• The temperature of the atmosphere does not stay the same throughout the year. It changes from season to season.
• In summers, it is hotter, while in winters, it is colder.
• This change happens because of the sun's energy that warms the Earth.
• The amount of sun's energy is different at different places on Earth, which is why some places are hotter than others.
• So, the temperature of the atmosphere changes, making the statement False.

Cold air is denser and heavy than warm air. The molecules are packed closer together. The amount of water vapor in the air also affects the density of the air. The more water vapor that is in the air, the less dense the air becomes. That is why cold, dry air is much heavier than warm, humid air.

The ozone layer is located in the stratosphere and plays a crucial role in shielding the Earth from the sun's harmful ultraviolet rays.

Topic in NCERT: Stratosphere

Line in NCERT: "One important feature of stratosphere is that it contains a layer of ozone gas."

Troposphere: It is the most important layer of the atmosphere. The air we breathe exists here. It has the following features:

• Its average height is 13 km.
• Almost all the weather phenomena occur in this layer. The weather phenomena include: Rainfall, Fog, Hailstorm etc.

Topic in NCERT: TROPOSPHERE

Line in NCERT: "Almost all the weather phenomena like rainfall, fog and hailstorm occur in this layer."

In the air we breathe, the most plentiful gas is nitrogen. It's important for plants to grow and for us to breathe. Nitrogen helps plants and animals to live. Hydrogen has least composition in air.

Topic in NCERT: COMPOSITION OF THE ATMOSPHERE

Line in NCERT: "Hydrogen are found in lesser quantities."