Some Natural Phenomena

Lightning

In this chapter, we discuss two destructive natural phenomena: lightning and earthquakes. We will also learn how to minimize their destructive effects.

What is Lightning?

• Example: Sparks on electric poles when wires are loose.
• Lightning is a large-scale electric spark.

Ancient Beliefs

• People were scared of lightning and thought it was the wrath of gods.
• Now we know lightning is due to the accumulation of charges in clouds.

Ancient Greeks and Electric Sparks

• Around 600 B.C., Greeks noticed amber (a type of resin) attracting light objects when rubbed with fur.
• Benjamin Franklin (1752) showed that lightning and the sparks from clothes are the same.

Understanding Electric Charges

• Example: Rubbing a plastic scale on dry hair makes it attract small pieces of paper.
• Everyday Example: When you take off woollen or polyester clothes, your hair stands up, and sometimes you see sparks in the dark.

Charging by Rubbing

Types of Charges and Their Interaction

Summary of Observations

• Like Charges Repel: Two charged balloons or two charged refills repel each other.
• Unlike Charges Attract: A charged balloon and a charged refill attract each other.

Types of Charges

• Positive and Negative Charges: Charges from rubbing a glass rod with silk are positive. Charges on a plastic straw rubbed with polythene are negative.
• Static Charges: Charges generated by rubbing are static and don’t move by themselves. Moving charges create electric current.

Now you know the basics of lightning and electric charges!

Transfer of Charge

Earthing

• Observation: Touching the paper clip with your hand makes the foil strips collapse.
• Explanation: The charge transfers to the earth through your body, discharging the foil strips. This process is called earthing and protects us from electrical shocks.

The Story of Lightning

• Formation of Charges:
  • During thunderstorms, air currents move upward and water droplets move downward.
  • This causes a separation of charges: positive charges at the top of clouds and negative charges at the bottom.
  • Positive charges also accumulate on the ground.
• Electric Discharge:
  • When charges become very large, they overcome air resistance.
  • Positive and negative charges meet, creating bright light and sound called lightning.
  • This can happen between clouds or between clouds and the earth.

Lightning Safety

• General Safety:
  • Hearing thunder means you should find a safe place immediately.
  • Wait a bit after the last thunder before leaving the safe place.

Finding a Safe Place

• Indoors: A house or building is safe.
• In Vehicles: Cars or buses are safe if windows and doors are shut.

Do’s and Don’ts During a Thunderstorm

• Outside:
  • Unsafe: Open vehicles (bikes, tractors), open fields, tall trees, shelters in parks, elevated places, carrying an umbrella.
  • Safe: Shelter under shorter trees if in a forest, stay far from trees and metal objects in open fields, squat low on the ground with hands on knees and head between hands to minimize target size.
• Inside the House:
  • Avoid contact with telephone cords, electrical wires, and metal pipes.
  • Use mobile or cordless phones instead of wired phones.
  • Avoid bathing and unplug electrical appliances like computers and TVs.
  • Keep electrical lights on as they are safe.

Lightning Conductors

• Function: Protect buildings from lightning.
• Structure: A metallic rod taller than the building, with one end in the air and the other buried in the ground.
• Benefit: Provides an easy route for electric charge to transfer to the ground.

By following these guidelines, we can stay safe during lightning and thunderstorms.

Earthquakes

You just learned about thunderstorms and lightning. These can cause a lot of damage, but they can be predicted to some extent. However, earthquakes are different because we can’t predict them accurately yet.

What is an Earthquake?

• Definition: A sudden shaking or trembling of the earth that lasts for a very short time.
• Cause: Disturbance deep inside the earth’s crust.
• Frequency: Earthquakes happen all the time, but major ones are rare.
• Impact: Can damage buildings, bridges, dams, and cause floods, landslides, and tsunamis.
• Example: Major earthquakes in India – 8 October 2005 in North Kashmir and 26 January 2001 in Bhuj, Gujarat.

What Causes an Earthquake?

• Earth’s Crust: The outer layer of the earth is not one piece; it’s fragmented into plates.
• Plate Movement: These plates are always moving. When they brush past each other or collide, they cause disturbances that result in earthquakes.

Other Causes of Tremors

• Volcanic Eruptions
• Meteor Hits
• Underground Nuclear Explosions

Seismic or Fault Zones

• Definition: Weak zones where earthquakes are more likely.
• In India: Kashmir, Western and Central Himalayas, North-East, Rann of Kutch, Rajasthan, Indo-Gangetic Plain, and some parts of South India.

Measuring Earthquakes

• Richter Scale: Measures the magnitude of earthquakes.
  • Destructive earthquakes have magnitudes higher than 7.
  • Example: Bhuj and Kashmir earthquakes had magnitudes greater than 7.5.

Seismic Waves and Seismograph

• Seismic Waves: Tremors produce waves on the earth’s surface.
• Seismograph: An instrument that records these waves.
  • It has a vibrating rod or pendulum with a pen that records the waves on paper.

More About the Richter Scale

• Not Linear: An increase of 2 in magnitude means 1000 times more destructive energy.
  • Example: An earthquake of magnitude 6 is 1000 times more destructive than one of magnitude 4.

Protection Against Earthquakes

Earthquakes cannot be predicted and can be very destructive. It’s important to take precautions, especially in seismic zones.

Building Safety

• Design: Buildings should be designed to withstand major tremors. Simple structures are more ‘Quake Safe’.
• Consult: Always consult qualified architects and structural engineers.
• Materials: Use mud or timber instead of heavy construction materials in highly seismic areas. Keep roofs light to minimize damage if they fall.
• Fixtures: Fix cupboards and shelves to walls to prevent them from falling.
• Placement: Be careful with wall clocks, photo frames, and water heaters to ensure they do not fall on people.
• Fire Safety: Ensure all buildings, especially tall ones, have working firefighting equipment.

Actions During an Earthquake

If You Are at Home

• Take Shelter: Get under a table and stay there until the shaking stops.
• Avoid Heavy Objects: Stay away from tall and heavy objects that might fall.
• In Bed: If you are in bed, do not get up. Protect your head with a pillow.

If You Are Outdoors

• Find a Clear Spot: Stay away from buildings, trees, and power lines. Drop to the ground.
• In a Vehicle: If you are in a car or bus, stay inside. Ask the driver to move slowly to a clear spot and stay inside until the tremors stop.

By following these guidelines, you can protect yourself and minimize the damage during an earthquake.

Chapter Summary:

• Some objects can be charged by rubbing with other objects.
• There are two kinds of charges — positive charge and negative charge.
• Like charges repel and unlike charges attract each other.
• The electrical charges produced by rubbing are called static charges.
• When charges move, they constitute an electric current.
• An electroscope may be used to detect whether a body is charged or not.
• The process of transfer of charge from a charged object to the earth is called earthing.
• The process of electric discharge between clouds and the earth or between different clouds causes lightning.
• Lightning strike could destroy life and property.
• Lightning conductors can protect buildings from the effects of lightning.
• An earthquake is a sudden shaking or trembling of the earth.
• Earthquake is caused by a disturbance deep inside the earth’s crust.
• It is not possible to predict the occurrence of an earthquake.
• Earthquakes tend to occur at the boundaries of earth’s plates. These boundaries are known as fault zones.
• Destructive energy of an earthquake is measured on the Richter scale. The earthquake measuring 7 or more on the Richter scale can cause severe damage to life and property.
• We should take necessary precautions to protect ourselves from earthquakes.

KEYWORDS

1. CRUST
2. DISCHARGE
3. EARTH’S PLATES
4. EARTHQUAKE
5. ELECTROSCOPE
6. LIGHTNING
7. LIGHTNING CONDUCTOR
8. NEGATIVE CHARGE
9. POSITIVE CHARGE
10. RICHTER SCALE
11. SEISMOGRAPH
12. THUNDER
13. THUNDERSTORM
14. TRANSFER OF CHARGE
15. TSUNAMI
16. TREMOR