The class 8 science chapter 15 discusses natural phenomena: lightning and earthquakes, and the measures to be taken to minimize the destruction caused by these phenomena. Let us take a look at some important points discussed in the chapter.
Lightning is an electric spark but on a huge scale. But before we understand the characteristics of lightning, let us a look at a few important points about charge:
- There are two types of charge – positive and negative charge.
- Unlike charges attract each other while like charges repel each other.
- An object can be charged by rubbing it with another object. The electrical charges acquired by rubbing is known as a static charge.
- When charges move, they constitute an electric current.
- An electroscope is used to detect whether a body is charged or not.
- The transfer of charge from a charged object to the earth is known as earthing.
- When a body loses charge to the earth, it is said to be discharged.
Formation of Lightning
- The water droplets move downward and the air current upward, during the development of a thunderstorm.
- These movements result in the separation of charges. The negative charges are collected at the lower edges of the clouds while the positive charges near the upper edges.
- When the magnitude of the gathered charges becomes large, the air no longer resists their flow. Positive and negative charges meet and give rise to streaks of bright light and sound. The resulting streaks are nothing but the lightning.
Lightning streak can destroy life and property, hence it is important to take protective measures against it in order to protect ourselves. A few safety measures against lightning are listed below:
- Find a safe place- A building or a house is safe. If inside a vehicle, close the windows and doors
- Do not carry umbrellas during thunderstorms
- Stay away from poles and metal objects
- If on the ground, do not lie on the ground, rather, squat low on the ground.
- Install lightning conductors on tall buildings, it allows an easy route for the transfer of electric charge to the ground.
An earthquake is the sudden shaking of earth that lasts for a short duration. It is caused because of the disturbance deep inside the earth’s crust. Earthquakes occur all the time all over the world. Only major earthquakes are noticed and are less frequent. Let us look at how an earthquake occurs:
- The outermost layer of the earth is fragmented and each fragment is known as a plate.
- The plates are in continuous movement.
- When a plate goes under another or brushes past against each other, a disturbance is caused in the earth’s crust.
- This disturbance shows up as an earthquake on the surface of the earth.
The boundaries of the plate are weak and are more to earthquakes. These weak zones are known as seismic or fault zones. Earthquakes can also be caused due to a volcanic eruption or when a meteor hits the earth. The magnitude of the Richter scale is used to express the power of an earthquake. The earthquake measuring 7 or more on a Richter scale is likely to cause severe damage to life and property. A few safety measures against the earthquake are:
- Take shelter under a table
- Find a clear spot, free of buildings, overhead power lines and trees. Drop to the ground.
- When on the ground, do not lie down, rather, squat low over the ground.
It is important to take necessary precautions to protect ourselves from earthquakes.
Some Natural Phenomena Class 8 Extra Questions
- Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
- List three states in India where earthquakes are more likely to strike.
- Explain why a charged body loses its charge if we touch it with our hand.
|NCERT Solutions for class 8 Science Chapter 15|
|NCERT Exemplar for class 8 Science Chapter 15|
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