Water in the Atmosphere
Class 11 · Geography
4 ideas in Class 11 Geography, explained in plain words, with games and quizzes to practise.
Humidity and Its Measures
Part of: Moisture in the air
Air holds invisible steam from zero to four parts in a hundred. The true weight per cube of air is absolute humidity. The share of full capacity at that heat is relative humidity. Fully loaded air is saturated, and the heat level where loading completes is the dew point. Warm air can hold far more than cold air.
Why it matters. Humidity rules comfort, fog, rain and health. These three terms turn muggy feelings into testable numbers.
Key words
- Absolute humidity
- : True vapour weight in each cube of air
- Relative humidity
- : Share of full vapour capacity at that heat
- Saturated air
- : Air holding all the vapour it can
- Dew point
- : Heat level where air turns fully loaded
- Vapour capacity
- : Maximum steam air can hold, rising with heat
Try it in two minutes
- Breathe on a cold mirror and watch drops bead.
- Call bead temperature the dew point of your breath.
- Wring a sponge half and full for relative shares.
- Compare sea air with desert air for capacity.
Try at home. Note three muggy and three dry moments in a week with possible causes.
From Vapour to Drops
Part of: Moisture in the air
Heat lifts liquid into vapour through evaporation, and wind speeds it by swapping wet layers for dry ones. Cooling reverses the trip: vapour beads on dust, smoke or salt specks or on cold objects. Ground beads above freezing make dew, icy beads make frost, ground-level clouds make fog, and thicker wet veils make mist.
Why it matters. Every drop of rain starts here. The pair explains dryers, dewdrops, foggy roads and frosty fields.
Key words
- Evaporation
- : Heat lifting of liquid water into vapour
- Condensation
- : Cooling return of vapour into liquid or ice
- Dew
- : Ground beads formed above freezing
- Frost
- : Icy beads formed below freezing
- Fog
- : Ground-touching cloud cutting sight below one km
Try it in two minutes
- Dry a wet cloth in sun versus shade for evaporation.
- Fan one half to show wind quickening.
- Chill a steel plate over ice for beading.
- Compare beads above and below freezing.
Try at home. Spot dew one cool morning and list the clear sky, calm air and long night behind it.
Clouds and Rain Birth
Part of: Clouds, rains and the world map
Clouds group by height and shape: feather-high cirrus, cotton-puff cumulus, blanket stratus and dark shapeless nimbus, with mixed children like towering storm heads. Drops fall when growth beats air hold. Warm falls give rain, frozen flakes give snow, half-melted pellets give sleet, and layered ice balls give hail.
Why it matters. Cloud reading forecasts hours ahead. Shape plus height tells coming rain better than any guess.
Key words
- Cirrus
- : High feather streaks of ice crystals
- Cumulus
- : Puffy cotton heaps with flat bases
- Stratus
- : Wide blanket layers veiling the sky
- Nimbus
- : Dark dense rain-bearing masses
- Hail
- : Layered ice balls from cold cloud trips
Try it in two minutes
- Spot feather streaks, puffs, blankets and dark bellies in sky photos.
- Rank them high to low.
- Shake pepper over steam as nuclei seeding.
- Drop beads till weight beats the updraft.
Try at home. Sketch four clouds seen in one week with height guesses and rain results.
World Rain Map
Part of: Clouds, rains and the world map
Rains fade poleward from the equator, favour coasts over interiors and seas over lands. Eastern shores drink deep near 35 to 40 degrees, western shores near 45 to 65 under westerlies, and wind faces of hills soak while lee faces starve. Belts run past 200 cm in wet tropics and monsoon coasts down to below 50 cm in shadows and high latitudes.
Why it matters. The map turns rainfall tables into reasons. Coasts, winds and hills explain each wet and dry belt.
Key words
- Poleward fade
- : Lessening of rains from equator to poles
- Windward soak
- : Heavy rains on the facing hill slope
- Rain shadow
- : Dry lee slope starved of rains
- Wet belt
- : Zone gaining over 200 cm yearly rains
- Dry belt
- : Zone gaining below 50 cm yearly rains
Try it in two minutes
- Trace equator-to-pole fading on a globe.
- Mark wet eastern shores and wet western mid shores.
- Shade hill wind faces dark and lee faces pale.
- Rank four belts from over 200 to below 50.
Try at home. Place your town in its belt and name the wind or hill rule behind its share.
What your child will practise
- Clouds and Rain Birth: Candy Quick Fire (Quick Fire)
- From Vapour to Drops: Desert Puzzle (Clue Puzzle)
- From Vapour to Drops: Desert Quick Fire (Quick Fire)
- Humidity and Its Measures: Space Quick Fire (Quick Fire)
- World Rain Map: Ocean Puzzle (Clue Puzzle)
- Quiz: Clouds and Rain Birth (8 questions)
- Quiz: From Vapour to Drops (8 questions)
- Quiz: Humidity and Its Measures (8 questions)
- Quiz: World Rain Map (8 questions)