Chapter 15: Some natural phenomena

These NCERT Class 8 Science Chapter 15 notes explain important natural phenomena like lightning and earthquakes in a clear and structured way. The chapter focuses on how these natural events occur and how they can cause damage.

It discusses electric discharge during thunderstorms, lightning conductors and safety measures during lightning. It also explains earthquakes, tectonic movements, focus, epicentre, seismic waves and measurement using the Richter scale.

Chapter 15 – Some Natural Phenomena is important for understanding disaster awareness and safety. It is highly relevant for school examinations and foundation level competitive preparation.

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1. Introduction to natural phenomena

• Natural phenomena are events that occur in nature without human control.
• Some natural phenomena are useful, while others become a disaster.
• Lightning and earthquakes are examples of natural phenomena.
• These events can cause loss of life and property.
• Understanding them helps in taking safety measures.

2. Lightning and thunderstorms

• Lightning is a natural electric discharge in the atmosphere.
• It occurs during a thunderstorm.
• Huge electric charges build up inside clouds.
• Lightning appears as a bright flash of light.
• It is followed by thunder due to rapid heating of air.

3. How lightning occurs

• During thunderstorms, clouds develop positive and negative electric charges.
• The upper part of the cloud becomes positively charged.
• The lower part becomes negatively charged.
• When the charge difference becomes very high, electric discharge occurs.
• This sudden discharge produces lightning.

4. Types and dangers of lightning

• Lightning can occur from cloud to cloud.
• Cloud-to-ground lightning is the most dangerous type.
• It can kill humans and animals.
• It may damage buildings and electrical appliances.
• Lightning can also cause forest fires.

5. Safety measures during lightning

• Stay indoors and avoid open areas during thunderstorms.
• Switch off electrical appliances to prevent damage.
• Do not stand under trees or carry metal objects.
• Avoid using mobile phones in open fields.
• Following lightning safety rules reduces risk.

6. Lightning conductor and earthing

• A lightning conductor is a device that protects buildings from lightning.
• It provides a safe path for electric charge to reach the ground.
• It consists of a metal rod fixed at the top of a building.
• The rod is connected to the ground by a thick wire.
• This process of safe discharge is called earthing.

7. Earthquake and its meaning

• An earthquake is the sudden shaking of the Earth.
• It is caused by disturbance inside the Earth’s crust.
• Earthquakes release large amounts of energy.
• The shaking can damage buildings and roads.
• Earthquakes occur without warning.

8. Causes and terms related to earthquake

• Movement of tectonic plates is the main cause of earthquakes.
• Volcanic eruptions and underground explosions can also cause earthquakes.
• The point inside Earth where the earthquake starts is called the focus.
• The point on Earth’s surface directly above the focus is the epicentre.
• Maximum damage usually occurs near the epicentre.

9. Seismic waves and measurement

• Energy released during earthquake travels as seismic waves.
• These waves cause shaking of the ground.
• A seismograph is used to record seismic waves.
• The Richter scale measures the magnitude of an earthquake.
• The scale usually ranges from 1 to 9.

10. Effects and safety during earthquake

• Earthquakes can cause loss of life and damage to buildings.
• Landslides and tsunamis may occur in some cases.
• During an earthquake, take shelter under a table.
• Move to open areas and stay away from buildings.
• Following earthquake safety measures reduces damage.

11. Earthquake-prone areas in India

• The Himalayan region is highly earthquake-prone.
• North-East India is also sensitive to earthquakes.
• Gujarat and parts of Rajasthan fall in seismic zones.
• Some parts of Bihar are earthquake-prone.
• India is divided into different seismic zones based on risk.

12. Key exam-oriented keywords explained

• Natural phenomena: Events that occur naturally without human control.
• Lightning: Sudden electric discharge in the atmosphere.
• Electric discharge: Flow of electric charge between clouds or to the ground.
• Thunderstorm: Storm with lightning and thunder.
• Lightning conductor: Device that protects buildings from lightning.
• Earthquake: Sudden shaking of Earth’s surface.
• Focus: Point inside Earth where earthquake begins.
• Epicentre: Point on Earth’s surface directly above the focus.
• Seismic waves: Waves produced by energy released during earthquake.
• Seismograph: Instrument used to record seismic waves.
• Richter scale: Scale used to measure earthquake magnitude.

13. One-page summary for quick revision

• Lightning is caused by electric discharge in clouds.
• Lightning conductors protect buildings through earthing.
• Earthquakes occur due to movements inside Earth’s crust.
• Focus and epicentre are key earthquake terms.
• Safety measures help reduce loss of life during disasters.

Understanding NCERT Class 8 Science Chapter 15 is essential to learn how lightning and earthquakes occur and how to stay safe during such events. The chapter clearly explains scientific causes and preventive measures.

The concepts help students develop disaster awareness and scientific understanding of natural events. It is highly useful for school exams and foundation competitive preparation.

Continue reading NCERT Class 8 Science Chapter 16 – Light to understand reflection and the human eye.

FAQs

Q1. What is lightning?
Lightning is a natural electric discharge that occurs in the atmosphere during thunderstorms.

Q2. What is a lightning conductor?
A lightning conductor is a device that protects buildings by providing a safe path for electric charges to reach the ground.

Q3. What is an earthquake?
An earthquake is the sudden shaking of the Earth caused by disturbances inside the Earth’s crust.

Q4. What is the difference between focus and epicentre?
The focus is the point inside the Earth where an earthquake starts, while the epicentre is the point on the surface directly above the focus.

Q5. Why is this chapter important for exams?
It explains lightning, earthquakes and safety measures, which are important for school exams and foundation preparation.

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