Lightning

Introduction:

• Lightning is a natural phenomenon involving electric sparks on a large scale.
• Similar to the sparks seen on electric poles or loose plugs, lightning is a massive electric spark.

Historical Perspective:

• In ancient times, people misunderstood lightning, associating it with the wrath of gods due to a lack of understanding.
• Modern science has explained that lightning is caused by the accumulation of charges in clouds.

Early Knowledge:

• Ancient Greeks, around 600 B.C., observed that rubbing amber with fur attracted light objects like hair.
• The phenomenon of hair standing on end and sparking when removing certain clothes in the dark was later connected to the principles of lightning.

Benjamin Franklin’s Contribution:

• In 1752, Benjamin Franklin, an American scientist, demonstrated the similarity between lightning and sparks from charged clothes.
• This realization marked a significant advancement in understanding electrical phenomena.

Nature of Electric Charges:

• To comprehend lightning, it’s essential to explore the properties of electric charges and their connection to atmospheric phenomena.

Practical Activities:

• Engaging in simple activities, such as rubbing a plastic scale on dry hair to attract small pieces of paper, helps in understanding the nature of electric charges.

Precautions:

• While lightning itself is not to be feared, precautions are necessary to protect against its potential dangers.
• Loose wires, especially during windy conditions, can generate sparks similar to lightning.

Charging by Rubbing

Process:

1. Plastic Refill and Polythene:
   • When a plastic refill is rubbed with polythene, both objects acquire a small electric charge.
   • The process results in the polythene and the refill being charged.
2. Plastic Comb and Dry Hair:
   • Rubbing a plastic comb with dry hair leads to the acquisition of a small electric charge by both objects.
   • In this case, the charging process affects both the comb and the hair.

Charged Objects:

• Objects that undergo the process of charging by rubbing are termed “charged objects.”

Types of Charges and Their Interaction

1. Balloon Interaction:
   • A charged balloon repelled another charged balloon.
   • A charged refill repelled another charged refill.
   • However, a charged balloon attracted a charged refill.

Interpretation and Questions:

• Different Types of Charges:
  • Does the repulsion and attraction observed indicate two kinds of charges?
  • Charges of the same kind repel each other, while charges of different kinds attract each other.
• Charge Convention:
  • It is convention to label the charge acquired by a glass rod rubbed with silk as positive.
  • The other type of charge is termed negative.
• Attraction Between Charged Objects:
  • When a charged glass rod is brought near a charged plastic straw rubbed with polythene, attraction is observed.
  • Indicates that the plastic straw carries a negative charge.

Additional Information:

• Static Nature of Charges:
  • The electrical charges generated by rubbing are static; they do not move by themselves.
  • Motion of charges constitutes an electric current.

Connection to Electricity:

• Electric Current:
  • The current in a circuit that powers a bulb or makes a wire hot is the motion of charges.

Transfer of Charge and Earth Connection

Charge Transfer:

• Aluminum foil strips receive the charge from a charged refill through a paper clip.
• Metals, like aluminum, are good conductors of electricity.
• Strips with similar charges repel each other, causing them to open wide.
• This device, called an electroscope, tests if an object carries a charge.

Charge Discharge:

• Touching the paper clip with a hand causes the foil strips to collapse.
• Foil strips lose charge to the earth through the body.
• This process of charge transfer to the earth is known as earthing.

Observations:

• Foil strips collapse when touched after charging due to charge loss to the earth.
• Repetition of charging and touching results in consistent collapse upon touch.

Importance of Earthing:

• Prevents the accumulation of excessive charge on objects.
• Ensures safety by providing a path for charge dissipation.

The Phenomenon of Lightning

Charge Separation in Thunderstorms:

• During a thunderstorm, air currents move upward, and water droplets move downward.
• These movements cause the separation of charges.
• Positive charges accumulate near the upper edges of clouds, and negative charges near the lower edges.
• Accumulation of positive charges also occurs near the ground.

Electric Discharge – Lightning:

• When accumulated charges reach a critical magnitude, air, usually a poor conductor, can no longer resist their flow.
• Negative and positive charges meet, resulting in streaks of bright light and sound.
• This visible phenomenon is known as lightning.
• The process is termed an electric discharge.

Occurrences of Electric Discharge:

• Electric discharge can happen between two or more clouds or between clouds and the earth.
• Lightning is a result of this discharge.

Understanding Lightning:

• Modern understanding allows us not to fear lightning as our ancestors did.
• Scientists continue to enhance their comprehension of this phenomenon.

Protection Measures:

• Despite understanding, lightning strikes can be destructive.
• Necessary measures should be taken to protect lives and property.

Lightning Safety Guidelines

During Lightning and Thunderstorm:

• No Open Place is Safe:
  • Open areas pose risks during thunderstorms.
• Alert to Rush to Safer Place:
  • Hearing thunder signals the need to find a safe location.
• Wait After Last Thunder:
  • Wait for some time even after the last thunder before leaving the safe place.

Finding a Safe Place:

• House or Building:
  • Considered a safe place during thunderstorms.
• In Vehicles:
  • Cars or buses with closed windows and doors provide safety.

Do’s and Don’ts During a Thunderstorm:

• Outside:
  • Avoid open vehicles and fields, tall trees, shelters in parks, and elevated places.
  • Carrying an umbrella is not advisable.
  • In a forest, seek shelter under shorter trees.
  • Stay away from metal objects, poles, and lie on the ground if no shelter is available.
• Inside the House:
  • Lightning can strike telephone cords, electrical wires, and metal pipes.
  • Avoid contact with these during a thunderstorm.
  • Unplug electrical appliances like computers and TVs.

Additional Lightning Safety Tips:

• Bathing:
  • Avoid bathing during thunderstorms to prevent contact with running water.
• Lightning Conductors:
  • Metallic rods taller than buildings, installed during construction, provide a route for electric charge transfer to the ground.
  • Metal columns, electrical wires, and water pipes in buildings offer some protection.
  • Avoid touching these during a thunderstorm.

Earthquakes: Nature’s Unpredictable Fury

What is an Earthquake?

• Definition:
  • Sudden shaking or trembling of the earth caused by a disturbance in the earth’s crust.
• Frequency:
  • Constant minor tremors occur worldwide, major earthquakes are less frequent but can cause significant damage.

Causes of Earthquakes

• Plate Tectonics:
  • Earth’s outer layer (crust) consists of fragmented plates in constant motion.
  • Disturbances occur when plates collide, brush past each other, or one goes under another.
• Plate Boundaries:
  • Weak zones or seismic fault zones at plate boundaries are prone to earthquakes.
  • India’s vulnerable areas include Kashmir, Western and Central Himalayas, North-East, Rann of Kutch, Rajasthan, Indo–Gangetic Plain, and parts of South India.

Earthquake Characteristics

• Impacts:
  • Can cause floods, landslides, and tsunamis.
  • Devastating tsunamis hit the Indian Ocean in 2004.
• Causes of Tremors:
  • Volcanic eruptions, meteor hits, underground nuclear explosions can also induce tremors.
  • Most earthquakes result from plate movements.

Predictability Challenges

• Plate Movement Predictions:
  • Despite understanding the cause, predicting when and where the next earthquake will occur remains challenging.
• Seismic Zones in India:
  • Identified seismic or fault zones in Kashmir, Western and Central Himalayas, North-East, Rann of Kutch, Rajasthan, Indo–Gangetic Plain, and parts of South India.

Magnitude and Destructiveness

• Magnitude Scale:
  • Richter scale measures earthquake power.
  • Destructive earthquakes have magnitudes above 7.
• Historical Examples:
  • Bhuj and Kashmir earthquakes had magnitudes exceeding 7.5.

Protection Against Earthquakes: Be Prepared, Stay Safe

Building Design

• Consult Professionals:
  • Engage qualified architects and structural engineers for earthquake-resistant building design.
• Simplicity is Key:
  • Design structures to be simple and ‘Quake Safe.’
  • Use lighter materials like mud or timber in highly seismic areas to minimize damage.

Interior Precautions

• Secure Furniture:
  • Fix cupboards and shelves to walls to prevent easy falling during tremors.
• Placement of Objects:
  • Carefully position items like wall clocks, photo frames, and water heaters to avoid injuries in case of falling.

Fire Safety Measures

• Fire Fighting Equipment:
  • Ensure all buildings, especially tall ones, have functional fire-fighting equipment, as earthquakes may lead to fires.

Quake-Resistant Housing

• Research and Development:
  • The Central Building Research Institute, Roorkee, has developed quake-resistant housing technology.

Action During an Earthquake

1. At Home:
   • Take shelter under a table until the shaking stops.
   • Stay away from tall and heavy objects to avoid falling hazards.
   • If in bed, stay put and protect your head with a pillow.
2. Outdoors:
   • Find a clear spot away from buildings, trees, and power lines.
   • Drop to the ground.
   • If in a vehicle, remain inside, asking the driver to move slowly to a clear spot.