1. What is Atmosphere?
The atmosphere is a blanket of air surrounding the Earth.
It contains gases, water vapour and dust particles and is held to the Earth by gravity.
हिंदी: Atmosphere = हवा की चादर, जो पूरी पृथ्वी को चारों ओर से घेरती है और गुरुत्वाकर्षण के कारण बंधी रहती है।
2. Composition of Atmosphere (Near Earth’s Surface)
Main gases:
- Nitrogen (N₂) – about 78%
- Oxygen (O₂) – about 21%
- Argon – about 0.93%
- Carbon dioxide (CO₂) – about 0.03–0.04%
हिंदी: याद रखने में मदद –
N₂ ≈ 78%, O₂ ≈ 21%, बाकी सब मिलाकर लगभग 1%
यानी 78 + 21 = 99% सिर्फ Nitrogen और Oxygen।
3. Importance of Major Gases
- Nitrogen – helps in plant growth (through nitrogen cycle).
- Oxygen – essential for respiration and burning.
- Carbon dioxide – used by plants in photosynthesis; also a greenhouse gas.
- Ozone (O₃) – absorbs harmful ultraviolet (UV) rays from the Sun.
हिंदी:
Ozone परत (O₃) हमें सूर्य की खतरनाक UV किरणों से बचाती है – NDA के लिए बहुत important point।
4. Layers of the Atmosphere (From Bottom to Top)
The atmosphere is divided into layers based on temperature changes with height:
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere (includes Ionosphere)
- Exosphere
5. Troposphere (Weather Layer)
- Lowest layer; extends up to about 8–18 km (higher at equator, lower at poles).
- Almost all weather phenomena occur here – clouds, rain, storms.
- Temperature generally decreases with height.
हिंदी: Troposphere = मौसम की परत (Weather layer)। बारिश, बादल, तूफान – सब यही परत में।
6. Stratosphere
- Lies above troposphere up to about 50 km.
- Contains the important ozone layer.
- Generally clear and stable; almost no storms.
- Good for flying of jet aircraft.
हिंदी: Ozone layer = Stratosphere में।
इसलिए कई jet planes इसी परत में उड़ते हैं क्योंकि मौसम अपेक्षाकृत स्थिर होता है।
7. Mesosphere
- Lies roughly between 50–80 km.
- Temperature decreases with height; very cold layer.
- Many meteors burn up in this layer.
8. Thermosphere (Includes Ionosphere)
- Extends roughly from 80 km upwards.
- Temperature increases with height (due to absorption of high-energy radiation).
- Ionosphere part contains charged particles (ions) – reflects radio waves, thus important for long-distance radio communication.
हिंदी: Ionosphere = radio संचार के लिए बहुत महत्वपूर्ण; यही radio signals को परावर्तित (reflect) करता है।
9. Exosphere
- Outermost boundary of the atmosphere.
- Very thin air; gradually merges into outer space.
10. Summary Table (Very Short)
Troposphere: 0–8/18 km – Weather, life-supporting, temp ↓ with height.
Stratosphere: up to ~50 km – Ozone layer, jets fly here.
Mesosphere: ~50–80 km – Meteors burn, very cold.
Thermosphere/Ionosphere: above ~80 km – radio waves, very hot.
Exosphere: outermost, merges with space.
Stratosphere: up to ~50 km – Ozone layer, jets fly here.
Mesosphere: ~50–80 km – Meteors burn, very cold.
Thermosphere/Ionosphere: above ~80 km – radio waves, very hot.
Exosphere: outermost, merges with space.
हिंदी Trick (नीचे से ऊपर):
“TSMTE” → Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere
इसे कई बार बोलें – याद हो जाएगा।
📘 Practice Questions (NDA Style)
1. The most abundant gas in the atmosphere is:
a) Oxygen b) Nitrogen c) Carbon dioxide d) Ozone
2. Nearly all weather phenomena occur in:
a) Stratosphere b) Mesosphere c) Troposphere d) Thermosphere
3. The ozone layer is mainly found in which layer?
a) Troposphere b) Stratosphere c) Mesosphere d) Exosphere
4. Which layer is most important for radio communication?
a) Troposphere b) Ionosphere (part of Thermosphere) c) Mesosphere d) Exosphere
5. The approximate percentage of Oxygen in the atmosphere is:
a) 10% b) 21% c) 50% d) 78%
a) Oxygen b) Nitrogen c) Carbon dioxide d) Ozone
2. Nearly all weather phenomena occur in:
a) Stratosphere b) Mesosphere c) Troposphere d) Thermosphere
3. The ozone layer is mainly found in which layer?
a) Troposphere b) Stratosphere c) Mesosphere d) Exosphere
4. Which layer is most important for radio communication?
a) Troposphere b) Ionosphere (part of Thermosphere) c) Mesosphere d) Exosphere
5. The approximate percentage of Oxygen in the atmosphere is:
a) 10% b) 21% c) 50% d) 78%
Answers:
1 – b) Nitrogen
2 – c) Troposphere
3 – b) Stratosphere
4 – b) Ionosphere (part of Thermosphere)
5 – b) 21%
1 – b) Nitrogen
2 – c) Troposphere
3 – b) Stratosphere
4 – b) Ionosphere (part of Thermosphere)
5 – b) 21%
Quick Recap | सार
Now you should be able to:
- Recall the most important ideas of this topic.
- Solve typical NDA-style questions from this chapter.
- Spot and avoid common traps used in competitive exams.
Self-check: 3–4 random questions उठा कर देखिए – अगर आसानी से हो रहे हैं, तो chapter strong है।
Common Exam Mistakes | आम गलतियाँ
- Concept ठीक से clear न करना और सीधे रटने की कोशिश करना।
- Question पूरी तरह पढ़े बिना answer mark कर देना।
- Figures, dates, या formulas को last step में verify न करना।
NDA में smart strategy यह है कि आसान वाले सवाल पहले, doubtful बाद में – और silly mistakes से बचना सबसे ज़रूरी है।