Class 11 Geography Chapter 8 – Composition and Structure of Atmosphere Notes in English | NCERT Solutions

Class 11 Geography Chapter 8 – Composition and Structure of Atmosphere Notes in English | NCERT Solutions

Atmosphere Notes
Published on By Amresh Academy

 

🌍 Class 11 Geography

✨ Chapter – 8 : Composition and Structure of Atmosphere

☁️ Atmosphere (वायुमंडल)

  • The cover of air around the Earth is called atmosphere.

  • This blanket of air is held due to Earth’s gravitational force (गुरुत्वाकर्षण बल).

  • Life on Earth is possible only because of this atmosphere.

  • About 99% of the atmosphere lies within 32 km above Earth’s surface.

🌬️ Air (वायु)

  • The mixture of different gases is called air.

  • It is colorless, odorless, and tasteless.

  • Important gases present – Nitrogen (78.8%), Oxygen (20.95%), Argon, Carbon dioxide, Neon, Helium, Ozone, Hydrogen, Methane, Krypton, Xenon etc.

  • Apart from gases, water vapor (जलवाष्प) and dust particles (धूल कण) are also present.

💨 Aerosols (एरोसॉल्स)

  • Combination of tiny water particles, carbon dioxide, ozone, noble gases and solid particles present in the air.

  • They help in cloud formation, rainfall, and scattering of sunlight.

🌐 Layers of the Atmosphere (वायुमंडल की परतें)

On the basis of temperature and air pressure (तापमान व वायुदाब), the atmosphere is divided into 5 layers:

  1. 🌎 Troposphere (क्षोभमंडल) – Closest to Earth, weather phenomena occur here.

  2. ☁️ Stratosphere (समतापमंडल) – Contains ozone layer that protects us from UV rays.

  3. 🌌 Mesosphere (मध्य मण्डल) – Meteors burn in this layer.

  4. 📡 Ionosphere (आयनमंडल) – Helps in radio communication by reflecting signals.

  5. 🚀 Exosphere (बहिर्मंडल) – Outermost layer, merges into outer space.

🧪 Composition of the Atmosphere (वायुमंडल की संरचना)

🔹 Gases (गैसें)

  • Nitrogen (78.8%) – Helps in protein formation for plants.

  • Oxygen (20.95%) – Life-giving gas, essential for breathing & burning.

  • Carbon Dioxide (0.03%) – Heaviest gas, found in lower layers, necessary for plants, absorbs heat.

  • Ozone (O₃) – Found at higher altitudes, absorbs harmful ultraviolet radiation.

💧 Water Vapor (जलवाष्प)

  • Amount depends on climate of a place.

  • Absorbs solar radiation (सौर विकिरण) and terrestrial heat (भौगोलिक ऊष्मा).

  • Prevents Earth from becoming too hot or too cold.

🌫️ Dust Particles (धूल कण)

  • Sources – soil, sea salt, smoke, ash, meteorite particles.

  • Act as nuclei for condensation (संघनन) → help in cloud formation & rainfall.

  • Scatter sunlight → create red & orange colors during sunrise and sunset.

🌟 Importance of Dust and Aerosols

  • ☁️ Cloud formation & rainfall

  • 🌞 Reflect sunlight → regulate temperature

  • 🌅 Create beautiful sunrise & sunset colors

  • 🌍 Maintain Earth’s heat balance

✨ In short: The atmosphere = gases + water vapor + dust particles + aerosols, which together make life possible on Earth 🌎.

✨ Composition & Structure of the Atmosphere

📊 Basis of Division of Atmosphere

  • On the basis of temperature & air pressure → 5 major layers.

  • On the basis of chemical composition → 2 broad layers:

    • Homosphere (होमोस्फीयर)

    • Heterosphere (हेटरोस्फीयर)

  • On the basis of temperature & gases → Atmosphere divided into Troposphere, Stratosphere, Mesosphere, Ionosphere & Exosphere.

☁️ Layers of the Atmosphere (वायुमंडल की परतें)

1️⃣ Troposphere (क्षोभमंडल)

  • Lowest layer of the atmosphere.

  • Average altitude: 13 km (18 km at equator 🌍, 8 km at poles ❄️).

  • All weather events like clouds ☁️, rainfall 🌧, winds 💨 occur here.

  • Most useful layer for human life.

2️⃣ Stratosphere (समतापमंडल)

  • Extent → up to 50 km.

  • Lower 20 km → no temperature change (isothermal zone).

  • Above 20 km → temperature increases with height.

  • Contains Ozone Layer (ओज़ोन परत) → absorbs harmful UV radiation ☀️.

3️⃣ Mesosphere (मध्यमंडल)

  • Extent → 50 to 90 km.

  • Temperature decreases with altitude.

  • Meteors ☄️ burn up in this layer.

4️⃣ Ionosphere (आयनमंडल)

  • Extent → 90 to 400 km.

  • Gas particles become electrically charged (ions) ⚡.

  • Important for radio communication 📡 → reflects radio waves back to Earth.

5️⃣ Exosphere (बाह्यमंडल)

  • Outermost layer 🚀.

  • Air density is extremely low → gradually merges into outer space.

⭐ Importance of the Troposphere

❓ Why is the Troposphere the most important layer?

  • Lowest layer, average altitude 13 km (18 km at equator, 8 km at poles).

  • Equator → higher height due to convective currents (संवहन धारा) that carry heat upward.

  • Contains maximum dust particles & water vapor.

  • All weather phenomena (clouds, condensation, rainfall, storms) occur here.

  • Temperature decreases with altitude → suitable for life.

💖 Why is the Troposphere called the Life-Giving Layer?

  • Provides all conditions necessary for life 🌱.

  • Contains oxygen & nitrogen → essential gases for living beings.

  • Controls winds, rainfall, clouds, and lightning ⚡.

  • Helps maintain Earth’s climate balance 🌍.

✨ Summary:
The Troposphere is the most important & life-giving layer of the atmosphere because it contains essential gases, weather activities, and conditions for survival. 🌏💨

☁️ Difference between Weather & Climate

🔄 Weather (मौसम)

  • Definition: The short-term (daily/weekly) atmospheric conditions of a small area.

  • Elements include → temperature 🌡, rainfall 🌧, air pressure 🌬, humidity 💧, wind direction & speed 🧭.

  • Represents short duration changes (hours to days).

🌤 Climate (जलवायु)

  • Definition: The long-term average of weather conditions over a large area and long period (30+ years).

  • Represents the general pattern of weather.

  • Based on studies of many years 📊.

📊 Key Difference (मुख्य अंतर)

Aspect

Weather 🌦

Climate 🌍

Meaning

Daily atmospheric condition

Long-term average condition

Time span

Short duration (hours to days)

Long duration (decades)

Area covered

Small region

Large region / whole globe

Stability

Changes quickly

Relatively stable

Example

"It rained today in Delhi" 🌧

"Delhi has hot summers & cold winters" ☀️❄️

🌡 Main Elements of Weather & Climate (मुख्य तत्व)

  1. Temperature (तापमान) 🌡

  2. Air Pressure & Wind (वायुदाब और पवन) 🌬

  3. Moisture & Precipitation (आर्द्रता और वर्षा) 💧🌧

🌍 Chief Climate Controllers (जलवायु के नियंत्रक कारक)

1️⃣ Latitude / Sun (अक्षांश / सूर्य की किरणें) ☀️
2️⃣ Distribution of Land & Water (भूमि और जल का वितरण) 🌊🏜
3️⃣ High & Low Pressure Belts (उच्च व निम्न दाब पट्टियाँ) 🌬
4️⃣ Altitude / Height (ऊँचाई) ⛰
5️⃣ Mountain Barriers (पर्वत अवरोध) 🏔
6️⃣ Ocean Currents (महासागरीय धाराएँ) 🌊

🌪 Other Different Types of Hurricane Winds (चक्रवाती पवन)

  • Cyclones (चक्रवात) 🌪

  • Typhoons (तूफ़ान – Pacific Ocean) 🌊

  • Tornadoes (बवंडर) 🌪

  • Hurricanes (Atlantic Ocean) 🌀

  • Willy-Willies (Australia) 🌪

✨ Summary:

  • Weather = short-term, local conditions 🌦.

  • Climate = long-term, regional/global patterns 🌍.

  • Both are controlled by temperature, pressure, moisture, and factors like latitude, altitude, oceans, and mountains.
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