Some Natural Phenomenon – Complete Guide for Class 8 Science Chapter 12

The chapter on Some Natural Phenomena in Class 8 Science introduces students to the fact that many everyday occurrences and natural events are governed by fundamental scientific principles. It covers various phenomena such as lightning, the chemical effects of currents, and earthquakes, illustrating how these events result from underlying physical and chemical processes. By exploring topics like the behavior of electric charges, the mechanisms behind lightning and thunderstorms, and the causes and effects of earthquakes, students gain a deeper understanding of the natural world. Understanding these events not only satisfies our curiosity but also helps us take necessary precautions.  

Lightning

Lightning is one of the oldest observed natural phenomena on Earth. It is a high-energy luminous electrical discharge from a thundercloud to the ground, accompanied by thunder. This atmospheric discharge of electricity typically occurs during thunderstorms, but can also happen during volcanic eruptions or dust storms.

Benjamin Franklin and Lightning

The study of natural phenomena, such as lightning, is exemplified by Benjamin Franklin’s pioneering work in the 18th century.  Benjamin Franklin showed that sparks share similarities with lightning. In June 1752, he raised a kite with his son Williams assisting. He attached a key to the end of the string and tied it to a post with a silk thread. As the string became soaked by rain, Franklin brought his hand close to the key and received a tingle of an electric shock, demonstrating the conductive properties of electricity.

Charging by Rubbing 

The concept of natural phenomena extends to the process of charging by rubbing, which demonstrates how everyday actions can reveal underlying scientific principles. When you rub a plastic comb on your dry hair, it can attract small pieces of paper. Similarly, rubbing a plastic scale with dry hair can give it a small charge. This process creates charged objects, indicating that charging involves both the comb and the hair acquiring charge.

Types of Charges and Their Interaction: Understanding natural phenomena involves exploring the types of electric charges and their interactions. Experiments show that there are two types of charges:

1. Like Charges: Charges of the same type repel each other.
2. Unlike Charges: Charges of different types attract each other.

For instance, a charged balloon repels another charged balloon but is attracted by a charged scale. The charge acquired by a glass rod when rubbed with wool is termed positive, while the opposite charge is negative. Static charges generated through rubbing do not move by themselves, unlike electric current which is the motion of charges.

How Charge is Transferred 

The transfer of charge in phenomena like lightning involves the movement of electrons between clouds and the ground. Similarly, understanding charge transfer through devices like electroscopes illustrates the principles behind these natural occurrences, emphasizing how the movement of charge is central to both everyday experiences and dramatic natural events.

An electroscope is a device used to test whether an object is carrying a charge. It operates on the principle that electrical charge can be transferred from one charged object to another through a metal conductor. An electroscope typically consists of an empty glass flask with a metallic rod and two metallic foils suspended from the rod. When a charged object is brought near the rod, the foils repel each other due to the transfer of charge.

Touching the rod with your hand discharges the foils as they lose charge to the earth through your body. This process of transferring charge to the earth is called earthing. Earthing is provided in buildings to protect against electrical shocks due to current leakage.

Story of Lightning

During natural phenomena like thunderstorms, air currents move upward while water droplets move downward, causing a separation of charges within the clouds. Positive charges collect near the upper edges, and negative charges accumulate near the lower edges. The ground also accumulates positive charges. When the charge accumulation becomes large, it overcomes the resistance of air, leading to an electric discharge between the clouds and the ground, visible as lightning.

Lightning Safety

Understanding natural phenomena like lightning underscores the importance of following safety measures during thunderstorms. To stay safe, seek shelter indoors and avoid contact with electrical wiring and metal objects.

During lightning or thunderstorms, follow these safety measures:

1. Indoor Safety Measures:
   • Avoid contact with electrical wires, telephone cords, and metal pipes.
   • Avoid bathing during lightning.
   • Use mobile or cordless phones instead of wired ones.
   • Unplug electrical appliances like computers and TVs.
2. Outdoor Safety Measures:
   • Avoid open vehicles and fields.
   • Stay away from tall trees and metallic objects.
   • Crouch on the ground with hands on knees and head between them if no shelter is available.

3. Lightning Conductors:
   • Install a lightning rod on buildings to provide a safe path for electrical discharge to the ground.

Earthquakes

Earthquakes are one of the most unpredictable and destructive natural phenomena. They result from disturbances deep inside the earth’s crust, causing vibrations that last for a short time. These disturbances are often caused by the movement of tectonic plates, either brushing against each other or colliding.

Causes of Earthquakes

Natural phenomena such as earthquakes are significant events that occur due to 

1. Tectonic Movements: The earth’s crust is fragmented into plates that are in continuous motion. When these plates brush aside one another or collide, they cause disturbances resulting in earthquakes.
2. Volcanic Activity: Explosive volcanic eruptions can also cause earthquakes, especially in areas of volcanic activity.

Measurement of Earthquakes

Natural phenomena like earthquakes produce seismic waves that are crucial for understanding the Earth’s internal processes. The magnitude of an earthquake is measured on the Richter scale. Earthquakes with magnitudes higher than 7 are considered very devastating.

Protection Against Earthquakes

To minimize the damage and ensure safety during an earthquake:

1. Building Safety:
   • Use lighter construction materials like mud or timber.
   • Fix cupboards and shelves to walls.
   • Equip buildings with fire-fighting equipment.
2. Personal Safety:
   • Indoors: Stay away from glass, get under sturdy furniture, and avoid rushing to exits.
   • Outdoors: Move to open spaces, away from buildings and tall structures.
   • In vehicles: Stay inside and ask the driver to move to a clear spot.

By understanding and respecting these natural phenomena, we can better prepare and protect ourselves from their potentially devastating effects. For instance, learning about the principles of electricity and charge interactions can inform safety measures during thunderstorms and lightning events. Similarly, comprehending the mechanisms and impacts of earthquakes allows for the development of more resilient infrastructure and effective emergency response plans. Education on these topics empowers communities to implement precautionary steps, such as constructing earthquake-resistant buildings and using lightning rods, thereby minimizing risks and enhancing overall safety. Through continued study and awareness, we can mitigate the damage caused by these powerful natural forces and safeguard lives and property.