Chapter: Some Natural Phenomena

• Introduction

  • Definition of natural phenomena
  • Destructive natural forces
  • Focus on Lightning and Earthquakes

• Lightning

  • Electric Charge
    • Concept of charging by rubbing (friction)
    • Discovery by Ancient Greeks (amber rubbed with fur)
    • Types of charges: Positive charge and Negative charge
    • Basic rule: Like charges repel, Unlike charges attract
  • Transfer of Charge
    • Role of electric current
    • Demonstration using an Electroscope
      • Principle: Like charges repel each other
      • Gold leaf or aluminum foil strips
    • Earthing
      • Transfer of charge from a charged object to the earth
      • Safety measure against electrical shocks
  • Lightning Story (Scientific Mechanism)
    • Accumulation of charges in clouds
    • Positive charges near upper edges, negative charges near lower edges
    • Accumulation near the ground too
    • Huge electric discharge (spark) producing lightning and thunder
  • Lightning Safety
    • Dos and Don'ts during a thunderstorm
    • Safe places: House, building, or a closed car
    • Unsafe places: Open fields, tall trees, umbrella with metallic end
    • Inside the house: Avoid corded phones, electrical appliances, and running water
  • Lightning Conductors
    • Safety device to protect tall buildings
    • Metallic rod installed at the top of the building
    • Provides easy path for electrical charge to flow to the ground

• Earthquakes

  • What is an Earthquake?
    • Sudden shaking or trembling of the earth
    • Lasts for a very short time
    • Causes: Major destruction of life and property (buildings, dams, bridges)
  • Causes of Earthquakes
    • Structure of the earth: Crust, Mantle, Core
    • Outer layer (Lithosphere) fragmented into plates (Tectonic plates)
    • Movement of plates: Grinding, sliding, or colliding
    • Seismic zones (fault zones) prone to earthquakes
  • Measurement of Earthquakes
    • Seismic waves generated by tremors
    • Recorded by an instrument called a Seismograph
    • Richter Scale
      • Magnitude scale to measure earthquake strength
      • Not linear (e.g., magnitude 6 has 1000 times more destructive energy than magnitude 4)
      • Destructive earthquakes measure 7 or more on the Richter Scale
  • Protection against Earthquakes
    • "Quake-safe" building construction in seismic zones
    • Consult qualified architects and structural engineers
    • Use mud or timber rather than heavy construction materials where possible
    • Safety Measures during an Earthquake
      • Drop, Cover, and Hold under a sturdy desk/table
      • Stay away from tall, heavy objects that may fall
      • If outdoors, move away from buildings, trees, and overhead power lines
      • If in a bed, stay there and protect your head with a pillow