📚 CHAPTER 2: UNDERSTANDING THE WEATHER

Class 7 | Exploring Society: India and Beyond

Notes + Worksheet with Answers

📝 STUDY NOTES

Weather = The state of the Earth’s atmosphere at a particular TIME and PLACE.

Atmosphere = The layer of gases (air) that surrounds the Earth.

Troposphere = Lowest layer of atmosphere (6–18 km high) where ALL weather happens & humans live.

• Thinner at the poles (cold air contracts) | Thicker at tropics (warm air expands)

🌡️ TEMPERATURE

Hot/cold? → Thermometer → Celsius (°C) or Fahrenheit (°F)

Formulas: Range = Max − Min | Mean = (Max + Min) ÷ 2

🌧️ PRECIPITATION

Rain/snow/sleet/hail? → Rain Gauge → measured in mm or cm

Depth of water collected in the cylinder = amount of rain

⚖️ ATMOSPHERIC PRESSURE

Weight of air? → Barometer → millibar (mb)

Normal = ~1013 mb at sea coast | Below 1000 mb = depression/storm

💨 WIND

Air movement from HIGH to LOW pressure

Direction → Wind Vane/Wind Sock | Speed → Anemometer (km/h)

💧 HUMIDITY

Water vapour in air? → Hygrometer → % Relative Humidity

Dry = 20–40% | Humid = 60–80% | 100% = fully saturated

Element

What it Measures

Instrument

Unit

Temperature

How hot or cold the air is

Thermometer

°C or °F

Precipitation

Amount of rainfall/snowfall

Rain Gauge

mm or cm

Atmospheric Pressure

Weight of air above us

Barometer

millibar (mb)

Wind

Direction and speed of air movement

Wind Vane + Anemometer

km/h (speed); N/S/E/W (direction)

Humidity

Amount of water vapour in air

Hygrometer

% (relative humidity)

Range of Temperature = Maximum Temperature − Minimum Temperature

Mean Daily Temperature = (Maximum + Minimum) ÷ 2

Scales: Celsius (°C) and Fahrenheit (°F). Example: 15°C = 59°F

Date

Max Temp (°C)

Min Temp (°C)

Range (Max−Min)

28.02.2025

29

16

13

01.03.2025

30

15

15

02.03.2025

31

17

14

03.03.2025

32

18

14

04.03.2025

30

17

13

05.03.2025

28

14

14

06.03.2025

29

15

14

From the table above:

• Highest Max Temp = 32°C (on 03.03.2025)

• Lowest Min Temp = 14°C (on 05.03.2025)

• Overall Range = 32 − 14 = 18°C

Precipitation = Any form of water that falls from the sky: Rain, Snow, Sleet, or Hail

• Measured using a RAIN GAUGE → funnel collects water → cylinder stores it → measuring scale reads the depth in mm

• If 5 mm of water is collected → the area received 5 mm of rainfall

Key terms: Sleet = frozen/partly frozen rain | Hail = small hard ice balls that fall like rain

Atmospheric Pressure = The weight/force of the air pressing down on the Earth’s surface.

• Instrument: Barometer | Unit: millibar (mb)

• Normal sea level pressure: ~1013 mb | Depression (storm forming): below 1000 mb

Location

Pressure

Effect

Sea coast / plains

~1013 mb (HIGH)

Normal breathing; comfortable

Mountain (e.g., 3000m)

~700 mb (LOWER)

Less oxygen; slight breathlessness

Khardung La, Ladakh (5600m)

~650 mb (VERY LOW)

Very hard to breathe; army pauses to acclimatise

Depression / Cyclone forming

Below 1000 mb

Storm/cyclone warning

Why breathless at high altitude? Less air = less oxygen → lungs work harder → feel dizzy/tired.

Acclimatise = Adjust slowly to new altitude/climate conditions. Travellers to high altitudes must take breaks.

Wind = Movement of air from HIGH pressure areas to LOW pressure areas.

Two important properties: SPEED (km/h) and DIRECTION (N, S, E, W)

Uses of Wind Data:

• Pilots & sailors use wind direction/speed for safe travel

• Farmers use it to predict rain direction

• Wind helps spread seeds (dandelion, cotton, etc.)

• Higher wind speed → soil dries faster

Humidity = Amount of water vapour (water in gas form) in the air.

Measured as RELATIVE HUMIDITY (%) using a HYGROMETER.

When humidity is high → water evaporates slowly → clothes dry slowly → we sweat more.

Relative Humidity

Weather Condition

Effect on Us

0%

Impossible in nature

—

20–40%

Dry weather

Clothes dry fast; skin feels dry

40–60%

Moderate / comfortable

Normal conditions

60–80%

Humid weather

Feels sticky; clothes dry slowly

100%

Fully saturated

Fog, clouds, or rain likely

Example: Delhi (52% humidity) vs Kochi (84% humidity)

→ Clothes dry FASTER in Delhi (lower humidity = more evaporation)

→ You sweat MORE in Kochi (high humidity = sweat can’t evaporate easily)

→ Kochi (coastal city) has higher humidity than Jaipur (inland desert city)

→ Humidity is also used in: food processing, museums (to protect exhibits), textiles

Nature’s Sign

What It Predicts

🐜 Ants carrying eggs to higher ground

Heavy rain expected

🐸 Frogs croaking loudly

Rain coming soon

🌲 Pine cones closing

Humid conditions; rain possible

🌲 Pine cones opening

Dry weather; seeds ready to spread

🐦 Birds flying low

Storm or rain approaching

🐿️ Squirrels gathering nuts rapidly

Harsh winter approaching

Weather Station = A place where all weather instruments are kept together to measure and track weather.

AWS (Automated Weather Station) = Self-operating; uses sensors; NO human needed; records all 5 elements automatically.

AWS is used in: Agriculture | Aviation | Navigation | Environmental monitoring | Disaster Management

Example: In 2023, NDMA set up an AWS at a glacial lake in Sikkim at 4800 m altitude for early warning.

Colour

Level

Action Required

🟢 GREEN

No Warning

All clear – no severe weather expected

🟡 YELLOW

Watch – Be Updated

Stay informed; check updates regularly

🟠 ORANGE

Alert – Be Prepared

Get ready; stock essentials; prepare to act

🔴 RED

Warning – Take Action

Immediate action needed; evacuate if required

Extreme Weather Events & the Dominant Element:

• July → Rainfall is dominant

• May & December → Temperature is dominant

• Cyclone forming → Atmospheric Pressure is dominant

• Loo (hot dusty winds in North India) / Forest fires → Wind is dominant

⚡ QUICK REVISION – KEY FACTS

Remember these!

• Weather = state of atmosphere at a particular time and place

• 5 Elements: Temperature | Precipitation | Atmospheric Pressure | Wind | Humidity

• Thermometer → Temperature (°C/°F) | Rain Gauge → Precipitation (mm)

• Barometer → Pressure (mb) | Wind Vane+Anemometer → Wind | Hygrometer → Humidity (%)

• Normal air pressure at sea level = 1013 mb | Below 1000 mb = depression

• Wind = air movement from HIGH to LOW pressure

• Relative Humidity: Dry = 20–40% | Humid = 60–80% | 100% = fully saturated

• IMD = India Meteorological Department, set up 1875

• Motto of IMD: ‘From the sun arises rain’ (Manusmriti)

• AWS = Automated Weather Station – self-operating with sensors

• IMD warning colours: Green (safe) → Yellow (watch) → Orange (alert) → Red (action)

• Range = Max − Min | Mean daily temp = (Max + Min) ÷ 2

📋 WORKSHEET – QUESTIONS & ANSWERS

SECTION A: In-Chapter Questions

✏️ Answer:

• Words like ‘hot’ or ‘cold’ are subjective – what feels cold to Krishnan in Chennai may feel pleasant to Amir in Kashmir.

• Without a common standard (like °C), two people cannot understand each other’s experience accurately.

• Precise measurement allows: scientific comparison, weather forecasting, planning activities like farming, travel, disaster management.

• Example: Saying ’20°C’ means the same thing to everyone everywhere.

✏️ Answer:

• The sun heats the surface of oceans, rivers, and land.

• This heat causes water to EVAPORATE and rise into the atmosphere as water vapour.

• As water vapour rises, it cools, condenses, and forms clouds.

• The clouds eventually release water as RAIN (precipitation).

• So: Sun’s heat → Evaporation → Water vapour → Clouds → Rain. ‘From the sun arises rain!’

✏️ Answer:

• As we go higher (e.g., climbing a mountain), there is LESS air above us.

• Less air = lower atmospheric pressure = less oxygen available per breath.

• With less oxygen entering the blood, the body has to work harder.

• This causes breathlessness, dizziness, and tiredness.

• Example: At Khardung La in Ladakh (5600 m), pressure is only ~650 mb vs 1013 mb at sea level.

• Solution: Acclimatise gradually – take rest breaks to let the body adjust.

✏️ Answer:

• Wet clothes dry faster in DELHI (52% humidity).

• Lower humidity means the air can absorb more water vapour → faster evaporation.

• In Kochi (84% humidity), the air is already full of moisture → evaporation is slow → clothes stay wet longer.

• Similarly, you sweat MORE in Kochi because sweat cannot evaporate easily in humid air.

✏️ Answer:

• Many plants rely on wind to spread their seeds (e.g., dandelion, cotton, grasses).

• Without wind, seeds would fall near the parent plant and compete for the same space, sunlight, and nutrients.

• Plant diversity in an area would reduce as seeds couldn’t travel to new places.

• Wind pollination would also stop, affecting reproduction of many plant species.

SECTION B: Exercise Questions (End of Chapter)

✏️ Answer:

(1) Hygrometer → (d) Humidity

(2) Anemometer → (c) Wind direction and speed

(3) Barometer → (b) Atmospheric pressure

(4) Thermometer → (e) Temperature

(5) Rain gauge → (a) Precipitation

✏️ Answer:

Advice for Jyotsna:

• Mumbai in June is HOT (29°C) and VERY HUMID (84%).

• She should pack: Light, breathable cotton clothes (not synthetic); carry an umbrella/raincoat (June is monsoon season in Mumbai).

• Avoid heavy dark-coloured clothes – they absorb heat.

• Expect to sweat a lot – carry a water bottle and stay hydrated.

• High humidity means she will feel hotter than 29°C actually is (heat + humidity = uncomfortable).

• Clothes may not dry easily if they get wet.

• Carry light footwear suitable for rain; avoid leather shoes.

✏️ Answer:

Best site: Option 3 – Open ground with elevated platform.

Why this is the best choice:

• Open ground ensures rain falls directly into the funnel without being blocked by trees or buildings.

• An elevated platform prevents flooding, splashing of ground water, or toppling by wind.

• The gauge must be on a FLAT, STABLE surface away from obstructions.

Why other options are NOT suitable:

• School vegetable garden: Plants may obstruct rainfall or cause splash readings.

• Terrace: Overhangs and walls may block some rain from falling into the funnel.

• Compound wall: Not flat/stable; rain might be blocked by the wall.

• Verandah: Covered area will NOT collect accurate rain data – most rain won’t reach it.

✏️ Answer:

Weather Report – Jammu & Kashmir – Evening of 01 February 2024

Good evening. Here is the weather report for Jammu and Kashmir today.

• SRINAGAR: Maximum temperature 6.5°C, minimum near 0°C. High humidity at 89%.

  Trace amounts of rainfall; light snowfall of 2.4 cm recorded.

• QAZIGUND: Much colder today, with max 3.2°C and minimum below zero at -0.4°C.

  Heavy precipitation: 11.8 mm rain and 10 cm snowfall. Very high humidity (97%).

• PAHALGAM: One of the coldest stations – max only 1.1°C, minimum -4.1°C.

  Significant snowfall of 8 cm and 6 mm of rain. Humidity at 96%.

• GULMARG: The coldest today! Below-freezing temperatures: max -2.6°C, min -7.6°C.

  Heavy snowfall of 6.35 cm and 8.2 mm rain. Humidity touching 100% by evening.

• MUZAFARABAD: Relatively warmer – 8.5°C max, 5.6°C min.

  Heavy rainfall of 25.8 mm; humidity 93%.

Overall, J&K experienced winter precipitation across all stations today,

with high humidity, snowfall, and below-normal temperatures at all stations.

SECTION C: Fill in the Blanks

Fill in the blanks:

1. Weather is the state of the Earth’s _____________ at a particular time and place. (Answer: atmosphere)

2. All weather phenomena take place in the _____________ layer of the atmosphere. (Answer: troposphere)

3. The instrument used to measure temperature is a _____________. (Answer: thermometer)

4. Rainfall is measured using a _____________. (Answer: rain gauge)

5. The weight of air pressing on Earth’s surface is called _____________. (Answer: atmospheric pressure)

6. The instrument used to measure atmospheric pressure is a _____________. (Answer: barometer)

7. The normal atmospheric pressure at sea coast is around _____________ mb. (Answer: 1013)

8. Wind is the movement of air from _____________ pressure to _____________ pressure. (Answer: high; low)

9. The speed of wind is measured by an _____________. (Answer: anemometer)

10. The amount of water vapour in the air is called _____________. (Answer: humidity)

11. Humidity is measured using a _____________. (Answer: hygrometer)

12. Dry weather has a relative humidity between _____% and _____%. (Answer: 20; 40)

13. The India Meteorological Department was set up in _____________. (Answer: 1875)

14. AWS stands for _____________. (Answer: Automated Weather Station)

15. The study of weather and its evolution is called _____________. (Answer: meteorology)

SECTION D: Match the Following

Column A

Column B (Answer)

Barometer

Measures atmospheric pressure (mb)

Anemometer

Measures wind speed (km/h)

Hygrometer

Measures relative humidity (%)

Rain Gauge

Measures precipitation (mm)

Wind Vane

Indicates wind direction

Thermometer

Measures temperature (°C/°F)

Troposphere

Layer where all weather occurs

Depression

Low pressure system below 1000 mb

AWS

Self-operating weather station

Loo

Hot, dry, dusty winds of North India

SECTION E: True or False

1. Weather is the permanent state of atmosphere at a place.  → FALSE – Weather changes frequently. The permanent average is called CLIMATE.

2. Thermometer measures atmospheric pressure.  → FALSE – Thermometer measures temperature. Barometer measures pressure.

3. All weather phenomena occur in the troposphere.  → TRUE

4. Normal atmospheric pressure at sea level is 1013 mb.  → TRUE

5. Higher wind speed causes soil to dry faster.  → TRUE

6. Higher humidity means clothes dry faster.  → FALSE – Higher humidity means slower evaporation, so clothes dry SLOWER.

7. Wind moves from low pressure to high pressure areas.  → FALSE – Wind moves from HIGH pressure to LOW pressure.

8. Pine cones close in dry weather to release seeds.  → FALSE – Pine cones OPEN in dry weather to release seeds; they CLOSE in humid conditions.

9. An AWS needs human operators to function.  → FALSE – AWS is self-operating (automated).

10. IMD’s motto means ‘From the sun arises rain’.  → TRUE

SECTION F: Short Answer Questions

✏️ Answer:

• Weather = state of atmosphere at a SPECIFIC TIME and PLACE (changes daily/hourly).

• Climate = the AVERAGE weather conditions of a place over a long period (30+ years).

• Example: ‘It is raining today’ = weather. ‘Mumbai has a wet monsoon season every year’ = climate.

✏️ Answer:

• Relative humidity is the percentage of water vapour in the air compared to maximum possible.

• 0% = completely dry air (impossible in nature).

• 100% = air is fully saturated with water vapour (fog, clouds, or rain is likely).

• It is measured using a hygrometer.

✏️ Answer:

• Climate change is making extreme weather (droughts, floods, cyclones) more frequent.

• Early warnings save lives – e.g., fishermen warned before storms; coastal areas evacuated before cyclones.

• Helps governments mobilise resources and prepare for disasters.

• Useful for: farming (crop planning), aviation (safe flying), tourism, sports events, military operations.

✏️ Answer:

• IMD collects weather data from all over India using instruments and AWS stations.

• It predicts weather and issues forecasts/warnings (using colour codes: green/yellow/orange/red).

• Was set up in 1875; its motto is ‘From the sun arises rain’.

• It issues warnings for heat waves, cold waves, cyclones, heavy rain, fog, etc.

• Helps fishermen, farmers, the aviation sector, and disaster management authorities.

📖 GLOSSARY – KEY TERMS

Term

Meaning

Weather

State of Earth’s atmosphere at a particular time and place

Atmosphere

Layer of gases (air) surrounding the Earth

Troposphere

Lowest layer of atmosphere (6–18 km); where all weather occurs

Temperature

How hot or cold the atmosphere is; measured in °C or °F

Precipitation

Any water from sky: rain, snow, sleet, or hail; measured in mm

Sleet

Frozen or partly frozen rain

Hail

Small, hard ice balls that fall like rain

Atmospheric Pressure

Weight of air above us; measured in millibar (mb) using barometer

Depression

Low-pressure system (below 1000 mb); can develop into storm/cyclone

Wind

Movement of air from high to low pressure areas

Humidity

Amount of water vapour in air; measured as relative humidity (%)

Water Vapour

Water in gaseous (gas) form

Thermometer

Measures temperature

Rain Gauge

Measures precipitation (rainfall) in mm

Barometer

Measures atmospheric pressure in millibar (mb)

Wind Vane

Shows wind direction; also called weather vane

Wind Sock

Wind vane at airports; helps pilots during take-off/landing

Anemometer

Measures wind speed in km/h

Hygrometer

Measures relative humidity (%)

Meteorology

Systematic study of weather and weather forecasting

Meteorologist

Scientist who studies and forecasts weather

Forecast

To predict weather conditions in advance

AWS

Automated Weather Station – self-operating weather data recorder

IMD

India Meteorological Department – set up 1875

Acclimatise

To adjust gradually to new altitude or climate

Relative Humidity

Humidity expressed as percentage; dry 20–40%, humid 60–80%

Loo

Hot, dry, dusty winds blowing in North India in summers

Statistics

Technique of gathering and analysing data to find patterns/predict

Ambient

Of the immediate surroundings (e.g., ambient temperature = room temperature)

🌤️ Weather affects every aspect of our lives – from what we wear to how we farm! 🌤️

Understanding weather helps us prepare, protect, and plan better.