Some natural phenomenons

SOME NATURAL PHENOMENA

Introduction

  • Discusses two destructive natural phenomena:

    • Lightning

    • Earthquakes

  • Importance of understanding these phenomena and taking precautions to minimize destruction.

12.1 Lightning

  • Observations of sparks from loose electric wires during wind or from loose plugs are small-scale representative of lightning.

  • Ancient beliefs associated lightning with divine wrath due to lack of understanding.

  • Current understanding attributes lightning to accumulation of electric charges in clouds.

Historical Context

  • Ancient Greeks (600 B.C.) observed phenomena of electric charges when amber was rubbed with fur.

  • Benjamin Franklin (1752): established similarity between lightning and static electricity from charged materials.

Properties of Electric Charges

  • Engaging activities designed to help understand electric charges and their behaviors.

  • Example: Rubbing a plastic scale on dry hair can cause attraction of small paper pieces.

12.2 Charging by Rubbing

  • Activity 12.1: Rub a ballpen refill with polythene, then observe its effect on small pieces of paper.

    • Charged objects include:

      • Plastic refills charged by polythene and hair.

      • Explore further with table comparing materials and their charging capabilities.

12.3 Types of Charges and Their Interaction

  • Activity 12.3: Inflating two balloons, rubbing them with wool, then observing repulsion or attraction

    • Like charges repel; unlike charges attract.

  • The convention of charge labeling:

    • Glass rod rubbed with silk = Positive charge.

    • Plastic straw rubbed with polythene = Negative charge.

12.4 Transfer of Charge

  • Activity 12.4: Create a simple electroscope to detect charges using a jam bottle and metal paper clip.

    • Observations: charged foil strips repel due to receiving the same charge.

  • Earthing: Transferring charge from a charged object to the earth through a conductor to prevent shocks.

12.5 The Story of Lightning

  • Explanation of lightning using charge separation during thunderstorms.

    • Upward air currents vs. downward water droplets during thunderstorms leading to charge accumulation.

  • Electric discharge causing visible lightning, significantly affecting life and property.

12.6 Lightning Safety

  • Guidelines to follow during lightning and thunderstorms:

    • Seek shelter indoors, avoid open spaces, tall trees, and conductors.

    • Adopt safety positions (squat low) if caught outdoors without shelter.

    • Electrical appliances should be unplugged during thunderstorms.

  • Lightning Conductor: Device installed on buildings to safely redirect electrical charge into the ground.

12.7 Earthquakes

  • Discusses key differences between lightning and earthquakes.

  • Earthquake Definition: A sudden shaking or trembling of the earth, often caused by inner earth disturbances.

  • Historical major earthquakes in India (Kashmir, Bhuj) are highlighted with the requirement for preparedness.

Causes of Earthquakes

  • Caused by disturbances in the earth's crust (fractured plates).

  • Major zones susceptible to earthquakes in India indicated.

  • Explanation of seismic waves associated with earthquakes, measured on the Richter scale where >7 indicates severe damage.

Protection Against Earthquakes

  • Recommendations for making buildings quake-resistant:

    • Design considerations for stability during tremors.

    • Advise on light structure materials for safety.

  • Specific safety actions during an earthquake:

    • Indoors: take cover under furniture.

    • Outdoors: move to open spaces away from structures.

KEYWORDS

  • Crust

  • Discharge

  • Earth's Plates

  • Earthquake

  • Electroscope

  • Lightning

  • Lightning Conductor

  • Negative Charge

  • Positive Charge

  • Richter Scale

  • Seismograph

  • Thunder

  • Thunderstorm

  • Transfer of Charge

  • Tsunami

  • Tremor

WHAT YOU HAVE LEARNT

  • Charging possible via rubbing; two types of charges.

  • Like charges repel, unlike charges attract.

  • Electroscope detects charge presence.

  • Lightning explained through charge separation.

  • Earthquakes can cause vast destruction; predictions are highly uncertain.

  • Safety precautions critical in seismic zones.