This MCQ module is based on: Thunderstorms, Cyclones and Safety
TOPIC 21 OF 50
Thunderstorms, Cyclones and Safety
🎓 Class 8
Science
CBSE
Theory
Ch 6 — Combustion and Flame
⏱ ~31 min
🌐 Language: [gtranslate]
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6.6 Thunderstorms and Lightning
On a hot summer afternoon, you may have noticed the sky suddenly darken, cool gusts of wind shake the trees, and a bright flash split the sky — followed seconds later by a rolling rumble. That is a thunderstorm — a spectacular display of atmospheric physics.
How Does a Thunderstorm Form?
Thunderstorms are common in hot, humid places. The recipe is simple:
- The Sun heats the ground strongly. The air just above it becomes hot and moist (because water evaporates from the soil, leaves, lakes and seas).
- This warm, moist air is lighter, so it rises rapidly.
- As it rises, it cools. The water vapour in it condenses into tiny droplets — forming clouds. Condensation releases heat.
- The released heat warms the surrounding air, which rises further and pulls up even more moist air from below.
- This runaway process builds enormous towering clouds (called cumulonimbus) that can be 10 km tall. Strong up-and-down air currents inside them rub droplets and ice crystals together, causing them to become electrically charged.
Lightning — an Electric Discharge
Inside these giant clouds, positive and negative charges get separated (positive near the top, negative near the bottom). When the voltage between different regions becomes huge enough to rip electrons through the air, a massive spark jumps — from cloud to cloud, or from cloud to the ground. This is lightning.
The temperature inside a lightning bolt can reach an astonishing 30,000 °C — hotter than the surface of the Sun! This intense heat causes the air in the channel to suddenly expand, then rapidly contract. The shock wave this produces is what we hear as thunder.
Why thunder comes after lightning: Light travels through air at about 300,000 km per second, while sound travels at only about 0.33 km per second. So although the lightning flash and the thunderclap happen at the same instant, the light reaches our eyes almost immediately, while the sound arrives a few seconds later.
Count Seconds → Estimate Distance
You can estimate how far a thunderstorm is by this simple rule:
\[ \text{Distance (km)} \approx \dfrac{\text{Seconds between flash and thunder}}{3} \]
So if you count 9 seconds between the flash and the sound, the storm is roughly 3 km away. If the number gets smaller with each bolt, the storm is moving towards you — seek shelter immediately.
Lightning Safety — Non-Negotiable!
✅ INDOORS — Do:
- Stay inside a closed building. Close windows and curtains.
- Unplug TVs, computers, refrigerators — surges can travel through wires.
- Stay off landline phones, metal plumbing and taps.
- Stay away from metal window frames and doors.
✅ OUTDOORS — Do:
- Seek shelter in a closed building or a car with closed windows (the metal body acts as a Faraday cage).
- If you cannot reach shelter, crouch low with your feet close together and hands on knees. Make yourself as small as possible — do not lie flat.
- If in a group, stay at least a few metres apart from each other.
🚫 Never:
- Take shelter under a tall, isolated tree — the tallest object in an area attracts lightning.
- Stand in an open field, swimming pool, pond or the sea.
- Hold or carry an umbrella, golf club or anything long and metallic.
- Ride bicycles or motorcycles during a storm.
Tall buildings have a lightning conductor — a thick copper rod fixed at the top and connected by a wire to a metal plate buried deep in the earth. If lightning hits the building, the rod gives the current a safe, low-resistance path into the ground, protecting the structure and the people inside.
6.7 Cyclones
A cyclone is nature on a terrifying scale — a spinning storm hundreds of kilometres wide, carrying winds that can flatten entire villages in minutes.
Structure of a Cyclone
Eye
The calm centre, 10–50 km across. Clear skies, almost no wind. Do not be fooled — it passes in 20–30 minutes and then the other side of the storm slams in.
Eyewall
The ring of the most violent winds and heaviest rain, just outside the eye. Wind speeds here can exceed 250 km/h.
Rain bands
Spiral arms of thundercloud wrapping around the eye, stretching hundreds of kilometres outward. They cause heavy rainfall over large regions.
How a Cyclone Forms
- Warm ocean: The surface temperature must be above about 26.5 °C. Warm sea water evaporates rapidly.
- Rising moist air: Hot, moist air above the ocean rises quickly, leaving a low-pressure region at the surface.
- Rushing winds: Surrounding higher-pressure air rushes in towards the low. Because the Earth rotates on its axis, the incoming winds are deflected — this is the Coriolis effect — and they start to spiral.
- Self-feeding cycle: More warm moist air is pulled up, condenses, releases heat, and the system spins faster. An eye forms, and the cyclone is born.
This is why cyclones are rare near the equator (the Coriolis effect is too weak there) and never form over cold oceans or over land (no warm ocean fuel).
Different Names for the Same Storm
| Name | Region |
|---|---|
| Cyclone | Indian Ocean, Bay of Bengal, Arabian Sea |
| Hurricane | Atlantic Ocean, eastern Pacific |
| Typhoon | Western Pacific Ocean |
| Willy-willy | Australia |
India's Cyclone-Prone Coasts
The Bay of Bengal is one of the most active cyclone basins in the world. Its shallow, warm waters and funnel shape make it especially dangerous. The eastern coast — Odisha, Andhra Pradesh, Tamil Nadu and West Bengal — is hit most often, usually between April–May and October–November. The Arabian Sea side (Gujarat, Maharashtra, Kerala coasts) is less active but storms there are increasing.
6.8 Cyclone Safety and Disaster Management
India's India Meteorological Department (IMD) uses satellites and radars to track cyclones days in advance and warns coastal districts. The National Disaster Management Authority (NDMA) coordinates the response — evacuating villages, stocking shelters, and rescuing stranded people.
Before the cyclone
Store drinking water, dry food and first-aid. Charge phones and torches. Tie down or bring in loose objects (flower pots, bicycles). Listen to radio/TV for official updates.
During the cyclone
Stay inside a strong building, away from windows and doors. Switch off electricity and gas. If flood water is rising, move to higher ground or a designated cyclone shelter. Do not step out when the eye passes — the storm isn't over!
After the cyclone
Do not touch fallen electric wires or puddles near them. Boil drinking water. Do not enter damaged buildings. Report injured persons and damage to the nearest helpline.
Recent Indian cyclones: Fani (2019, Odisha), Amphan (2020, West Bengal–Odisha), Tauktae (2021, Gujarat–Maharashtra), Biparjoy (2023, Gujarat). Thanks to modern forecasting and timely evacuation of lakhs of people, loss of life in recent cyclones has been far lower than in the catastrophic cyclones of the past.
🔬 Activity — Make a Family Cyclone Safety PlanL6 Create
🤔 Think first: If your area were to be hit by a cyclone next week, what would your family need to do today?
- With your family, list the 3 safest rooms in your home (away from windows, on a lower floor).
- Make an emergency kit: torch, batteries, radio, whistle, drinking water, biscuits/dry food, basic medicines, important documents in a waterproof bag.
- Identify your nearest cyclone shelter and the shortest safe route to reach it.
- Save the numbers of your local disaster helpline, hospital and police station.
- Practise: when alerted, how many minutes does it take your family to be ready to move?
Most cyclone casualties happen because people do not have a plan — they panic, take too long to evacuate, or ignore warnings. A simple rehearsed plan like the one above can literally save lives in the critical hours before a cyclone strikes.
🎯 Cyclone & Lightning Safety Quiz L3 Apply
Q1. You are in an open field when lightning starts. The nearest building is 2 km away. What is the BEST thing to do?
Run fast under the nearest tall tree Crouch low with feet together, hands on knees Lie flat on the ground Hold up your metal umbrellaQ2. During a cyclone, you notice the wind and rain stop suddenly and the sky briefly clears. What should you do?
Rush outside to check on neighbours — the storm is over Stay indoors — you are in the eye; the other side of the storm is coming Open all the windows for fresh airQ3. You count 6 seconds between a lightning flash and the thunderclap. Roughly how far is the storm?
About 6 km About 2 km About 18 kmQ4. After a cyclone, you see a fallen electric wire in a puddle. What should you do?
Push it aside with a stick Keep well away, alert the authorities Walk carefully around the edge of the puddle📋 Competency-Based Questions
Meera lives in a coastal village in Odisha. In October the IMD issues a cyclone warning — wind speeds of 180 km/h expected in 36 hours. The village is evacuated to a concrete cyclone shelter inland. That night Meera sees lightning flashes and counts 9 seconds before the thunderclap. During the cyclone's passage, there is a sudden half-hour of eerie calm before winds return even stronger.
Q1. L1 Remember Name the agency in India that issues cyclone warnings.
India Meteorological Department (IMD). Disaster response is coordinated by the National Disaster Management Authority (NDMA).
Q2. L2 Understand Using the counting rule, how far away is the lightning Meera sees?
Answer: B. Distance ≈ 9 ÷ 3 = 3 km.
Q3. L3 Apply Why should Meera NOT step outside during the half-hour of calm?
That calm is the eye of the cyclone — the centre of the storm passing overhead. In 20–30 minutes the other side of the eyewall (with equally violent winds, possibly from the opposite direction) will strike.
Q4. L4 Analyse Why is the Bay of Bengal more cyclone-prone than the Arabian Sea?
The Bay of Bengal is shallower and warmer than the Arabian Sea, giving more evaporation fuel for cyclones. Its funnel shape also pushes storm surges onto the coast. The Arabian Sea is deeper and cooler, and historically produced fewer storms (though this is changing with climate change).
Q5. L5 Evaluate A neighbour says: "Cyclones cannot form right on the equator because the Earth's rotation doesn't affect air there." Is this scientifically correct?
Largely correct. The Coriolis effect due to Earth's rotation is essentially zero at the equator and grows with latitude. Without Coriolis, incoming air cannot be deflected into a spiral, so cyclones almost never form within about 5° of the equator, even if other conditions (warm ocean, moisture) are met.
🔗 Assertion–Reason Questions
Assertion (A): Thunder is heard a few seconds after lightning is seen.
Reason (R): The speed of light is much greater than the speed of sound in air.
Answer: A. Light takes almost no time, while sound takes about 3 seconds per km — hence the lag.
Assertion (A): During a thunderstorm, one should not shelter under a tall isolated tree.
Reason (R): Lightning tends to strike the tallest object in the area.
Answer: A. A tall lone tree offers the shortest path to ground and is a prime target.
Assertion (A): Cyclones form only over warm ocean waters.
Reason (R): Warm water evaporates rapidly and supplies the moist air that fuels the storm's updrafts.
Answer: A. Sea surface above ~26.5 °C is the essential fuel for cyclone formation.
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