Class 11 Geography (Fundamental of Physical Geography) Chapter 7 Composition And Structure Of Atmosphere

Key Concept: Pressure Belts

c) Uneven heating of the Earth’s surface by the Sun

[Solution Description] The main reason for the formation of pressure belts on Earth is the uneven heating of the Earth’s surface by sunlight. Equatorial regions receive more direct sunlight, creating low-pressure zones due to rising air, while polar areas receive less sunlight, leading to high-pressure zones with sinking air.

Key Concept: Basic Concept

c) Ozone

[Solution Description] The ozone layer is located in the stratosphere and plays a crucial role in absorbing the majority of the sun’s harmful UV rays. This absorption prevents these rays from reaching the Earth’s surface, thus protecting living organisms.

Key Concept: Distribution of dust particles

c) Subtropical and temperate regions.

[Solution Description] Dust particles tend to have higher concentrations in subtropical and temperate regions due to various climatic and topographical factors that facilitate their accumulation and suspension.

Key Concept: Basic Concept

b) 2°C

[Solution Description]

The rate of temperature decrease in the troposphere is given as 1°C for every 165 meters of ascent. To find the temperature decrease over 330 meters, we calculate how many increments of 165 meters are there in 330 meters:

$\frac{330 \text{ meters}}{165 \text{ meters}} = 2$

This means that in 330 meters, the temperature decreases by $2 \times 1^\circ$C, which equals 2°C.

Key Concept: Important Layer

b) Stratosphere

[Solution Description] The stratosphere is the layer of the atmosphere that contains the ozone layer. This layer is crucial for absorbing and scattering the sun’s ultraviolet solar radiation, thereby protecting life on Earth from harmful UV rays.

Key Concept: Major Gas

d) Nitrogen

[Solution Description] The atmosphere is primarily composed of nitrogen, which makes up a significant portion of it.

Key Concept: Equatorial vs Polar

b) It decreases consistently.

[Solution Description] Water vapour concentrations are higher in warm tropical regions and decrease toward the colder polar regions due to changing temperatures and humidity levels from the equator towards the poles.

Key Concept: Layer Characteristics

a) Troposphere

[Solution Description] Dust particles are known to be more concentrated in the lower layers of the atmosphere, primarily in the troposphere. This is because the troposphere is closest to the Earth’s surface where these particles originate from various sources like soil, sea salts, smoke, etc.

Key Concept: Ozone Layer Function

b) To absorb ultraviolet radiation

[Solution Description] The primary function of the ozone layer is to absorb harmful ultraviolet (UV) radiation from the sun. Without this absorption, UV radiation would reach the Earth’s surface in much higher quantities, which could lead to increased instances of skin cancer, cataracts, and other health issues, as well as harm to ecosystems.

Key Concept: Water Vapour Distribution

c) Tropics

[Solution Description] Water vapour is most abundant in the tropics due to high temperatures and large bodies of water that lead to significant evaporation. Warm air holds more moisture, contributing to increased water vapour concentration in tropical regions compared to other areas like deserts or poles.

Key Concept: Greenhouse Effect

d) Carbon Dioxide

[Solution Description] Carbon dioxide is significant in the greenhouse effect as it traps terrestrial radiation, helping maintain Earth’s temperature.

Key Concept: Oxygen Quantity

c) 120 km

[Solution Description] According to the syllabus, the concentration of oxygen becomes negligible above 120 km. Therefore, the correct option is based on altitude.

Key Concept: Advanced Cause and Effect, Concept Integration

d) They facilitate cloud droplet formation but don’t guarantee significant rainfall.

[Solution Description] Dust particles can serve as condensation nuclei in clouds, facilitating droplet formation necessary for precipitation. However, in desert regions where humidity is low, even if dust particles are present, they may not lead to significant precipitation due to insufficient moisture. Thus, while dust can promote droplet nucleation, the lack of atmospheric moisture limits rain production.

Key Concept: Water Vapour Variation

b) Decreases

[Solution Description] As altitude increases, the temperature tends to decrease, which reduces the air’s capacity to hold water vapour. Consequently, water vapour content generally decreases with increasing altitude.

Key Concept: Temperature Trend

c) Mesosphere

[Solution Description] The mesosphere is the atmospheric layer located above the stratosphere that extends from 50 km to 80 km. In this layer, the temperature decreases with altitude, reaching as low as -100°C at around 80 km. Therefore, the correct answer is the mesosphere.

Key Concept: Dust and Climate

c) Act as hygroscopic nuclei for clouds

[Solution Description] Dust particles act as hygroscopic nuclei around which water vapour condenses, leading to cloud formation. They also influence the absorption and reflection of sunlight, thereby affecting climate and weather patterns.

Key Concept: Presence of Electrically Charged Ions

c) Between 80 and 400 km

[Solution Description] The ionosphere is located between 80 and 400 km above the mesopause. It is a crucial part of the Earth’s atmosphere containing ions that reflect radio waves.

Key Concept: Gas Composition

d) Nitrogen

[Solution Description] The major gas that constitutes the largest portion of the Earth’s atmosphere is Nitrogen, which accounts for 78\% of the atmospheric composition.

Key Concept: Basic Definition

c) Gases, water vapour, and dust particles

[Solution Description] The atmosphere is a mixture of gases, water vapour, and dust particles.

Key Concept: Environmental Impact

b) Contributes to acid rain, affecting ecosystems

[Solution Description] Increased levels of sulfur dioxide $(SO_2)$ in the atmosphere contribute significantly to acid rain formation, which has adverse effects on ecosystems by lowering soil pH, damaging plant life, and causing harm to aquatic organisms.

Key Concept: Major Gas

b) Nitrogen

[Solution Description] The major gas in Earth’s atmosphere is nitrogen, which makes up approximately 78\% of the atmosphere by volume.

Key Concept: Layer Identification

d) Ionosphere

[Solution Description] The ionosphere, located approximately between 80 km and 400 km above Earth’s surface, is responsible for reflecting radio waves, making it essential for effective communication over long distances.

Key Concept: Basic Gases

c) Carbon dioxide

[Solution Description] Carbon dioxide ($$CO_2$$) is a crucial component in the atmosphere responsible for the greenhouse effect as it absorbs and reflects terrestrial radiation, thereby warming the Earth.

Key Concept: Humidity and Weather Impact

b) It decreases

[Solution Description] Relative humidity is defined as the ratio of the current absolute humidity to the highest possible absolute humidity at that temperature. When the air temperature rises, the capacity of air to hold water vapor increases, causing the relative humidity to decrease if the water vapor content remains the same.

Key Concept: Dust and Climate

c) By acting as hygroscopic nuclei

[Solution Description] Dust particles act as hygroscopic nuclei, attracting moisture from the air. This process facilitates the condensation of water vapor around the dust particles, leading to cloud formation. Hygroscopic nuclei are essential in cloud physics because they provide surfaces for the water droplets to form, which eventually leads to cloud development.

Key Concept: Basic Layers

c) Ionosphere

[Solution Description] The ionosphere is the region of the Earth’s atmosphere that contains a high concentration of ions and free electrons and is capable of reflecting radio waves back to Earth. It is located in the thermosphere.

Key Concept: Altitude Range

b) 10-50 km

[Solution Description] According to the syllabus, the ozone layer is located within the stratosphere at an altitude range of 10-50 km above Earth’s surface. This answer requires direct recall of this specific information mentioned.

Key Concept: Pressure Belts and Winds

c) Subtropical regions

[Solution Description] Trade winds are persistent east-to-west winds found in the tropics just north and south of the equator. They result from high-pressure systems in subtropical zones moving towards low-pressure areas around the equator. The most consistent trade winds are typically found between about 5° and 30° latitude in both hemispheres.

Key Concept: Altitude Effects

d) Temperature decreases steadily with altitude

[Solution Description] Temperature decreases with altitude in the troposphere at a rate of 1°C per 165m. This decrease affects air density and helps create conditions suitable for cloud formation and weather changes.

Key Concept: Layer Function

c) Stratosphere

[Solution Description] The stratosphere contains the ozone layer, which plays a critical role in absorbing harmful ultraviolet radiation from the sun.

Key Concept: Basic Concepts

b) Altitude

[Solution Description] The factors controlling temperature include latitude, altitude, distance from the sea, ocean currents, and prevailing winds. Latitude determines how much solar energy an area receives; therefore, it directly impacts temperature.

Key Concept: Boundary Recognition

c) Mesopause

[Solution Description] The correct name for the boundary between the mesosphere and the thermosphere is the “mesopause.” This is a specific term used to describe that transition point in the atmosphere.

Key Concept: Basic Layers

b) Stratosphere

[Solution Description] The ozone layer is located in the stratosphere, where it absorbs the majority of the sun’s harmful ultraviolet radiation.

Key Concept: Basic Composition

d) Carbon Dioxide

[Solution Description] Carbon dioxide is known to be a significant contributor to the greenhouse effect as it absorbs and reflects terrestrial radiation.

Key Concept: Pressure Belts

d) Equatorial low

[Solution Description] The Equatorial low-pressure belt, also known as the doldrums, is characterized by rising air and low pressure at the equator due to intense solar heating.

Key Concept: Layer Composition

d) Ionosphere

[Solution Description]

The layer containing electrically charged particles, commonly referred to as ions, is the ionosphere.

Key Concept: Temperature Gradient

a) 0.0061°C per meter

[Solution Description] In the troposphere, the temperature decreases at a rate of 1°C for every 165 meters of altitude.

Key Concept: Ozone Function, Structure of Atmosphere

b) It absorbs ultraviolet radiation, preventing harmful exposure.

[Solution Description] The ozone layer within the stratosphere plays a critical protective role for life on Earth by absorbing the majority of the Sun’s harmful ultraviolet (UV) radiation. UV radiation can cause skin cancer and cataracts in humans, and it can also harm marine ecosystems and terrestrial plant life. By filtering out these UV rays, the ozone layer minimizes their damaging effects, thus allowing life to thrive on Earth.

Key Concept: Temperature Influence

c) Temperature increases with altitude.

[Solution Description] In the stratosphere, the temperature increases with altitude. This is primarily due to the ozone layer absorbing ultraviolet radiation, which adds heat to the atmosphere and results in a temperature increase.

Key Concept: Atmospheric Layers

b) Stratosphere

[Solution Description] The stratosphere is the layer of the atmosphere that contains the ozone layer, which absorbs most of the Sun’s harmful ultraviolet radiation. This helps protect living organisms on Earth.

Key Concept: Dust Particles

a) Troposphere

[Solution Description] The syllabus states that dust particles are concentrated in the lower atmosphere, particularly in the troposphere.

Key Concept: Basic Definition

b) Absorbs ultraviolet radiation

[Solution Description] The main function of the ozone layer is to absorb ultraviolet (UV) radiation from the Sun, which protects living organisms on Earth by preventing harmful UV rays from reaching the surface.

Key Concept: Troposphere Characteristics

c) It contains most of the atmospheric water vapour and dust.

[Solution Description] The troposphere contains most of the atmosphere’s water vapour and dust, which are critical for weather variations. These elements contribute to cloud formation and precipitation, making the troposphere a key layer for weather activities.