Some Natural Phenomena
Overview
Lightning — the sky's biggest spark — and earthquakes — the ground shaking beneath us. Both are natural phenomena — learn the science behind both and the safety rules for each.
Typed Notes
Charge — from rubbing
When two objects are rubbed together — electrons move from one to the other — one becomes positive (gave away electrons), the other becomes negative (gained electrons). Glass rod + silk: glass becomes positive, silk becomes negative. Plastic comb + dry hair: comb becomes negative — it attracts small pieces of paper. Rule: like charges repel (− and −), unlike charges attract (+ and −). An electroscope is an instrument used to detect charge (two thin strips — they spread apart when charged). This is static electricity — seen as dust sticking to a TV screen or a crackling sound from a sweater.
How lightning is formed
Inside large clouds, ice crystals and water droplets are pushed up and down by air currents — friction causes charges to separate: positive charge at the top, negative charge at the bottom (charge separation). When the charge builds up too much — the air (which is an insulator) breaks down — a huge spark occurs in the sky: lightning (light). That same spark heats the surrounding air rapidly, causing it to expand — producing thunder (the loud boom). Light travels first (300 million m/s), sound travels later (340 m/s) — that is why we see lightning before we hear thunder — the time gap helps us estimate the distance.
Lightning conductor and safety
A lightning conductor consists of a pointed metal rod placed at the highest point of a building → connected by a thick copper wire → to a metal plate buried in the ground. When charge accumulates — it flows safely into the ground through the wire — the building is not damaged (Benjamin Franklin demonstrated this through his kite experiment — important: do not try this at home today!). Safety during a storm: (1) Stay indoors — keep away from windows and doors, avoid metal objects, wired appliances, and landline phones; (2) In open areas — stay away from isolated tall trees, towers, and electric poles (charge tends to strike them), move to an open area — crouch down (feet together, kneel, head down); (3) Inside a car you are safe (the metal body carries charge to the outside); (4) Stay away from water — avoid bathing or touching water taps.
Earthquake — safety
An earthquake is caused by the sudden movement of tectonic plates — this generates waves — making the ground shake. Measurement: a seismograph measures the waves (magnitude — Richter scale; 5 or above causes damage). Safety: (1) Indoors — get under a table or bed, move near a strong beam or corner of a wall — stay away from objects that may fall; (2) Outdoors — move to an open field — away from buildings, trees, and electric poles; (3) NEVER use a lift (if electricity fails — you will be trapped); (4) In a vehicle — move away from bridges and tunnels; (5) Afterwards — aftershocks (smaller tremors) also occur. Japan conducts earthquake drills every month — we should do the same in our schools.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Charging by rubbing: rub two objects together — charge transfer occurs: glass rod + silk = positive charge; plastic + wool = negative charge. Like charges repel, unlike charges attract.
- 02Lightning: ice crystals and water droplets collide inside clouds — charges separate (positive at top, negative at bottom) — when charge builds up too much — a giant spark in the sky — lightning (+ sound = thunder).
- 03Lightning conductor: a pointed metal rod on the roof of a building → connected by a thick wire → to the ground (earth) — charge safely flows into the earth — building is protected (Franklin's kite experiment).
- 04Safety during thunderstorm: stay indoors (avoid metal objects, wired phones), outdoors — stay away from tall trees and towers, stay safe inside a car (Faraday cage effect), crouch down in open areas.
- 05Earthquake: movement of tectonic plates — measured by seismograph (magnitude — Richter scale); safety: indoors — get under a table or near a beam, outdoors — move to an open field, NEVER use a lift.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
How does charging by rubbing work? Explain with the example of a glass rod and silk.
Lightning is seen first and thunder is heard later — why?
How does a lightning conductor work?
What should you do if you are caught in an open field during a thunderstorm?
What should you do if you are indoors during an earthquake?
What does a seismograph do?
Rubbing causes charge (like charges repel, unlike charges attract). Lightning: charge separation inside clouds — spark + thunder (light first, sound later). Lightning conductor: pointed rod → wire → earth — protects the building. Safety: during a storm — stay indoors or in a car, in open areas stay away from trees and crouch. Earthquake: measured by seismograph; indoors — get under a table, outdoors — move to an open field, never use a lift.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.When a glass rod is rubbed with silk, what charge does the glass rod acquire?
Q2.What is the function of a lightning conductor?
Q3.What is the most dangerous thing to do during an earthquake?
Q4.Why is it safe to be inside a car during a thunderstorm?
Mark karo — dashboard par progress dikhega.