Composition and Structure of Atmosphere
Class 11 · Geography
4 ideas in Class 11 Geography, explained in plain words, with games and quizzes to practise.
Gases of the Air
Part of: What air is made of
Air mixes steady gases with changing ones. Carbon dioxide lets sun rays pass in but traps earth heat going out, warming the air like a greenhouse lid. Ozone sitting 10 to 50 km up drinks harmful sun rays before they land. Oxygen fades by 120 km height, and carbon dioxide plus vapour stay below 90 km.
Why it matters. These gases decide warmth and safety. Small shifts in them explain big climate news without any mystery.
Key words
- Carbon dioxide
- : Gas passing sun rays in but trapping earth heat out
- Greenhouse lid
- : Trapping of outgoing heat warming the air
- Ozone screen
- : Layer drinking harmful sun rays high above
- Fossil fuel rise
- : Extra carbon gas from burning old fuels
- Gas ceiling
- : Height above which a gas turns negligible
Try it in two minutes
- Hold clear glass over a warm plate as sun rays entering.
- Cover the plate and feel heat staying like trapped rays.
- Name carbon dioxide as the lid and ozone as the shield.
- Ask what burning fuels adds to the lid.
Try at home. List three gases with one job each: warmer, shield and breather.
Water Vapour and Dust
Part of: What air is made of
Water vapour shifts with place and height: near four parts in wet tropics, below one in dry cold lands, falling poleward and upward. It blankets warmth and steadies air. Dust from seas, soils, smoke, pollen and fallen meteors floats thickest in dry windy belts and seeds clouds when vapour beads on salt and dust grains.
Why it matters. Vapour and dust run rain and skies. Their shifts explain humid coasts, dry deserts and cloudy days.
Key words
- Vapour blanket
- : Steam cover steadying warmth day and night
- Poleward fall
- : Lessening of vapour from equator to poles
- Dry belt dust
- : Thick floating grains in windy subtropical lands
- Seed grain
- : Salt or dust speck beading vapour into cloud drops
- Air steadiness
- : Calm or restless state tuned by vapour
Try it in two minutes
- Boil water and watch steam fade with height above the pot.
- Call the fade the vapour fall with height.
- Shake chalk dust in light and watch bits float.
- Breathe on a cold spoon to seed drops like clouds.
Try at home. Note morning haze versus noon clarity for three days and link it with vapour and dust.
Layers of the Sky
Part of: Layers and weather elements
The troposphere is the lowest sheet, about 13 km deep, holding all weather, dust and vapour; it cools about one degree per 165 m and stretches higher over the hot equator. Above sit the stratosphere with its ozone shield to 50 km, the chilling mesosphere to 80 km, the ion layer bouncing radio waves between 80 and 400 km, and the fading exosphere melting into space.
Why it matters. Layer order fixes where planes fly, where weather brews and where radios bounce. Mixing layers scrambles all three.
Key words
- Troposphere
- : Lowest sheet holding weather, dust and vapour
- Tropopause
- : Steady lid capping the lowest sheet
- Stratosphere
- : Second sheet holding the ozone shield
- Ion layer
- : Charged sheet bouncing radio waves back
- Exosphere
- : Fading top sheet melting into space
Try it in two minutes
- Stack five books as air layers on a table.
- Slip weather, shield, chill, radio and fade tags on them.
- Make the bottom book thicker at the hot side.
- Bounce a ball off the fourth book as radio echo.
Try at home. Draw five stacked bands and write one job plus one height number in each.
Elements of Weather and Climate
Part of: Layers and weather elements
Six changeable elements rule daily skies: temperature, pressure, winds, humidity, clouds and rain. They shift hourly and steer crops, clothes, flights and health. The steady gas mix matters too, but geographers chase these six first, giving them three full chapters next. The lowest two air sheets host nearly all their action.
Why it matters. Naming the six turns vague sky talk into sharp study. Each later chapter then owns one slice of the six.
Key words
- Temperature
- : Heat level of air steering comfort and crops
- Pressure
- : Weight of air driving winds and storms
- Humidity
- : Steam share of air felt as dampness
- Cloud cover
- : Beaded vapour veils shading and raining
- Precipitation
- : Falling water in rain, snow or hail forms
Try it in two minutes
- Step out and feel heat, breeze and dampness.
- Name temperature, wind and humidity from feelings.
- Spot clouds and guess coming rain.
- Link pressure maps with coming winds.
Try at home. Keep a four-day diary of heat, wind, dampness and rain using the six names.
What your child will practise
- Elements of Weather and Climate: Candy Quick Fire (Quick Fire)
- Gases of the Air: Desert Puzzle (Clue Puzzle)
- Gases of the Air: Desert Quick Fire (Quick Fire)
- Layers of the Sky: Space Quick Fire (Quick Fire)
- Water Vapour and Dust: Ocean Puzzle (Clue Puzzle)
- Quiz: Elements of Weather and Climate (8 questions)
- Quiz: Gases of the Air (8 questions)
- Quiz: Layers of the Sky (8 questions)
- Quiz: Water Vapour and Dust (8 questions)