Chapter 15: Some Natural Phenomena
कुछ प्राकृतिक परिघटनाएँ (तड़ित, विद्युतदर्शी, भूकम्प, सिस्मोग्राफ एवं रिक्टर पैमाना)
Don't Let a 20-Minute Bubbling Delay Cost You CTET Qualification
In offline CTET exams, bubbling 150 bubbles takes 18 to 22 minutes of mechanical time. A single misaligned row can trigger an 8-question domino error. Practice bubble-filling this chapter's solved MCQs inside Mentora's official OMR simulator.
- Static Electricity by Friction: When amber is rubbed with fur or a plastic comb with dry hair, it acquires static electric charge. A glass rod rubbed with silk acquires a POSITIVE charge; an ebonite or plastic straw rubbed with polythene acquires a NEGATIVE charge.
- Fundamental Electrostatic Law: Like charges repel each other; unlike charges attract each other.
- Electroscope (विद्युतदर्शी): A device used to test whether an object is carrying electric charge. Two thin strips of gold or aluminum foil suspended on a metal rod inside a glass jar diverge (repel each other) when charged.
- Earthing (भू-सम्पर्कण): The process of transferring electrical charge from a charged body directly into the earth. Used in residential building wiring to protect against electric shocks caused by current leakage.
- Lightning & Lightning Conductor (तड़ित चालक):
- - Lightning is a massive natural electric spark discharge between clouds of opposite charges or between clouds and earth.
- - Lightning Conductor: A thick metal rod taller than the building installed inside walls during construction. Its upper sharp pointed spike projects into open air; its bottom connects to a copper plate buried deep in the earth, providing an effortless harmless path for lightning discharge into ground.
- Lightning Safety Protocols:
- - DO NOT carry an umbrella with a metallic rod/tip in open fields.
- - If caught in an open field with no shelter: SQUAT LOW on the ground with hands on knees and head tucked between knees (NEVER lie flat on ground; do NOT stand under isolated tall trees).
- - Inside a car or bus: SAFE, provided windows and doors are closed (Faraday cage effect).
- Earthquakes & Seismic Scales:
- - Caused by sudden movement, sliding, or colliding of lithospheric tectonic plates along fault lines (Seismic Zones).
- - Seismograph (भूकंपलेखी): Instrument that records seismic tremors.
- - Richter Scale (रिक्टर पैमाना): Logarithmic scale measuring destructive earthquake energy. An increase of 2 units on Richter scale means $1,000\times$ more destructive energy (e.g. magnitude 7 releases 1,000 times more energy than magnitude 5, NOT $1.4\times$!).
- Trap: Richter scale is linear (magnitude 6 is twice magnitude 3). FALSE: Richter scale is LOGARITHMIC; an increase of 2 on the scale corresponds to $1,000\times$ the destructive power.
- Trap: During an outdoor thunderstorm with lightning, what is the safest posture? Correct: SQUAT LOW with hands on knees and head tucked between hands; NEVER lie flat on ground.
- Trap: A glass rod rubbed with silk acquires which charge? Correct: POSITIVE charge.
NCERT Core Facts: Atmospheric Electrostatics & Seismology
Lightning protection principles and Richter scale physics appear reliably in CTET Paper 2:
1. Electrostatic Charging by Friction
[Glass Rod rubbed with Silk] ──> Acquires POSITIVE (+) Charge
[Plastic Comb / Straw rubbed] ──> Acquires NEGATIVE (-) Charge
Like Charges Repel ( + with + , - with - )
Unlike Charges Attract ( + with - )2. Logarithmic Physics of the Richter Scale
- The Richter scale is NOT linear.
- An increase of 2 in magnitude means:
- An earthquake of magnitude 7.0 releases over $1,000$ times the destructive seismic energy of a magnitude 5.0 earthquake!
3. Lightning Conductor Operation
- Installed on high-rise buildings during masonry work.
- The top spike ionizes local charge, while the continuous heavy metallic strip directs lightning strike current straight into a buried copper grounding plate, preventing structural fire and electrocution.
Test Your Mastery: Some Natural Phenomena
Authentic CBSE exam questions tested directly from this NCERT chapter.
An earthquake of magnitude 7 on the Richter scale releases approximately how much more destructive seismic energy compared to an earthquake of magnitude 5?
रिक्टर पैमाने पर 7 तीव्रता का भूकंप 5 तीव्रता के भूकंप की तुलना में लगभग कितनी अधिक विनाशकारी भूकंपीय ऊर्जा छोड़ता है?
If a person is caught outdoors in an open field during an intense thunderstorm with lightning and cannot find a building, what is the safest recommended posture according to NCERT?
यदि कोई व्यक्ति बिजली के साथ तेज गरज के दौरान खुले मैदान में फंस जाता है और कोई इमारत नहीं ढूंढ पाता है, तो NCERT के अनुसार सबसे सुरक्षित अनुशंसित स्थिति क्या है?
Why should a person caught in an open field during a thunderstorm never stand under an isolated tall tree?
Lightning preferentially strikes the tallest object in an open area to find the shortest path to ground, making isolated tall trees lethal lightning targets.
How much more destructive energy is released by a magnitude 7 earthquake compared to a magnitude 5 earthquake on the Richter scale?
Approximately 1,000 times more energy, because the Richter scale is logarithmic where each increase of 2 units corresponds to a thousand-fold energy jump.