CBSE Class 8 Science Notes Chapter 12 Some Natural Phenomena

Lightning: Introduction

Lightning occurs during thunderstorms when air currents move upwards while water droplets move downwards, causing a separation of charges within the clouds and between the clouds and the Earth. As the magnitude of these charges increases, the normally non-conductive air becomes a conductor, allowing the flow of electricity. This flow of charge, accompanied by bright light and sound, is known as lightning.

Electric Discharge

Electric discharge refers to the flow of charge between clouds or from a cloud to the Earth due to the separation of positive and negative charges. This process results in the visible and audible phenomena associated with lightning.

Lightning Safety: Steps to Follow

Outside the House:

• Find shelter under small trees or safe structures.
• If inside a vehicle, stay inside with doors and windows closed.
• Avoid metal poles and do not lie flat on the ground; instead, crouch with your head between your hands.

Inside the House:

• Avoid using telephones or touching electrical wires.
• Refrain from bathing.
• Unplug electrical appliances to prevent damage or injury.

Lightning Conductors

Lightning conductors are devices installed on buildings to protect them during lightning strikes. They consist of a tall metal rod that extends from the top of the building to the ground, providing a direct path for the electric discharge to safely reach the Earth.

Earthquakes

An earthquake is a sudden shaking of the Earth's surface caused by disturbances deep within the Earth's crust. These natural disasters can cause significant damage to life and property and cannot be predicted with certainty.

Causes of Earthquakes

Earthquakes occur due to the movement or collision of tectonic plates in the Earth's crust. The Earth's crust is divided into several large plates that constantly move. When these plates collide, slide past each other, or collapse under one another, they can cause earthquakes on the surface.

Seismic/Fault Zones

The boundaries between tectonic plates are known as seismic or fault zones. These areas are particularly susceptible to earthquakes because they are weaker points where stress can accumulate and eventually be released as seismic activity.

Power of Earthquakes

The strength of an earthquake is measured using the Richter Scale. An earthquake with a magnitude greater than 7 on this scale is considered destructive. The Richter Scale is logarithmic, meaning that each whole number increase on the scale represents a thousandfold increase in energy released.

Seismic Waves

Tremors from earthquakes produce waves known as seismic waves. These waves travel through the Earth's crust and are recorded by instruments called seismographs. A seismograph uses a vibrating rod or pendulum to detect and record the seismic waves.

Protection from Earthquakes: Steps to Follow

Outdoors:

• Move to a clear area away from buildings and overhead lines.
• If you are in a vehicle, pull over to a safe location and remain inside the car until the shaking stops.

Indoors:

• Take cover under a sturdy table or desk and stay there until the shaking ceases.
• Avoid standing near tall or heavy objects that might fall.

Structural Measures:

• In seismic areas, build structures with lightweight roofs to reduce damage.
• Secure shelves and cupboards to walls.
• Ensure that buildings are equipped with functional firefighting equipment, as fires can occur after an earthquake.

Benefits of CBSE Class 8 Science Notes Chapter 12

• Comprehensive Understanding : These notes provide a thorough overview of natural phenomena such as lightning and earthquakes. They cover fundamental concepts, causes, and effects, helping students grasp the intricate details of these events.
• Clear Explanations : The notes simplify complex topics making them easier for students to understand. By breaking down the concepts into manageable sections, they ensure that students can follow and retain the information effectively.
• Foundation for Advanced Learning : Understanding these basic concepts prepares students for more advanced studies in natural sciences. The knowledge gained from this chapter serves as a foundation for exploring more complex phenomena in higher classes.
• Exam Preparation : The notes are structured to align with the CBSE curriculum, making them a valuable resource for exam preparation. They help students focus on key points and revise efficiently, improving their performance in assessments.
• Encourages Critical Thinking : By exploring the causes and effects of natural phenomena, students develop critical thinking skills. They learn to analyze and interpret scientific information, which is essential for problem-solving and scientific inquiry.
• Enhanced Learning Experience : The notes are prepared by subject experts, ensuring accuracy and relevance. This expertise contributes to a richer learning experience, providing students with reliable and well-organized study material.