NCERT Class 8 Science Chapter 12 ‘Some Natural Phenomena’: Notes and Solutions (Free PDF) 

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NCERT Class 8 Science Chapter 12

The chapters of NCERT become easy to understand when we have well-written notes. The value of these notes increases during the exam season. Hence, keeping the same in mind, we have prepared Solutions and Notes for NCERT Class 8 Science Chapter 12: Some Natural Phenomena. These will help you cover the entire chapter and serve as a quick revision method. The PDF of important questions and answers is also available for you to download. Let’s explore the same now.

Chapter 1Chapter 2Chapter 3
Chapter 4Chapter 5Chapter 6
Chapter 7Chapter 8Chapter 9
Chapter 10Chapter 11Chapter 12
Chapter 13

NCERT Class 8 Science Chapter 12: Lightning and Electric Charge Notes

In this NCERT Class 8 Science Chapter 12, we will learn about lightning, transfer of charge, Earthquakes, etc. Let’s begin.

Lightning

Lightning is caused by the accumulation of charges in the clouds.

  • The ancient Greeks knew as early as 600 B.C. that when amber (amber is a kind of resin) was rubbed with fur, it attracted light objects such as hair.
  • In 1752 Benjamin Franklin, an American scientist, showed that lightning and the spark from your clothes are essentially the same phenomena. However, it took 2000 years for this realisation to occur.

Charging by Rubbing

When we rub a plastic refill with polythene, it acquires a small electric charge. Similarly, when we rub a comb on dry hair, it acquires a charge. These are known as charged objects

Types of Charges and Their Interaction

Here are different types of charges and their interactions:

  • Basically, there are two types of charges: Positive and Negative.
  • When a glass rod is rubbed with silk, then by convention, the charge acquired by it is called positive. The charge on the other object would be negative.
  • It is observed that when a charged glass rod is brought near a charged plastic straw rubbed with polythene there is attraction between the two. This clearly shows that there is a negative charge acquired by the straw.
  • The electrical charges generated by rubbing are static meaning they don’t move by themselves.
  • Movement of charges constitutes of electric current.
Class 8 Science Chapter 12: Some Natural Phenomena: Charges

Also Read:- What is a Natural Disaster? Types, Causes, Events

Transfer of Charge

Electrical charge can be transferred from one charged object to another through a metal conductor. 

  • The process of transferring charge from a charged object to the earth is called Earthing.
  • An electroscope is a device that is used to detect whether an object is carrying a charge or not. 

The Story of Lightning

Here is how lightning occurs:

  • During the development of a thunderstorm, the air currents move upward while the water droplets move downward.
  • Due to vigorous movements, the charges separate. 
  • Positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. 
  • There is an accumulation of positive charges near the ground also.
  • When the magnitude of these charges becomes a lot, then the charges start to flow.
  • This produces streaks of bright light and sound as lightning.
  • This process is called an electric discharge.
  • The process of electric discharge can occur between two or more clouds, or between clouds and the earth.
Class 8 Science Chapter 12: Some Natural Phenomena: Lightning

Lightning Safety

Let us explore key points related to safety during lightning:

  • No open place is safe during lightning and thunderstorms.
  • On hearing the sound of lightning, we should rush to a safer place. A house or a building is a safe place. If you are travelling by car or by bus, you are safe inside with windows and doors of the vehicle shut.
  • After hearing the last thunder, wait for some time before coming out of the safe place.

Do’s and Don’ts during a Thunderstorm

In this section, we will learn about do’s and don’ts during a thunderstorm.

Outside 

  • Open vehicles are not safe such as motorbikes, open cars, etc. So, avoid travelling in them.
  • Elevated places do not protect us from lightning strokes so avoid those. 
  • Don’t carry an umbrella during a thunderstorm as it may conduct the electricity to you. 
  • If you are in a forest, take shelter under shorter trees.
  • If no shelter is available and you are in an open field, stay far away from all trees, poles or other metal objects.
  • Do not lie on the ground. Instead, squat low on the ground. Place your hands on your knees with your head between the hands. This position will make you the smallest target to be struck.

Inside

  • Lightning can strike telephone cords, electrical wires and metal pipes, so avoid using them during a thunderstorm.
  • It is safer to use mobile phones and cordless phones.
  • Bathing should be avoided during thunderstorms to avoid contact with running water because water conducts electricity.
  • Electrical appliances like computers, TVs, etc., should be unplugged.
  • Electrical lights can remain on.

Lightning Conductors

  • A lightning conductor is a device that is used to protect the building from lightning.
  • It is a long metal rod that is taller than the building installed in the walls of the building with one end free in the air and the other one buried deep inside the Earth. 
  • Through the rod the electric charge passes down into the Earth, thus preventing any damage. 

Also Read:- Essay on Disaster Management

NCERT Class 8 Science Chapter 12: Earthquake Notes

In this section of NCERT Class 8 Science Chapter 12 we will learn about Earthquakes, how are they caused, and related topics. Let’s start. 

What is an Earthquake?

The sudden shaking and trembling of the Earth due to the disturbance deep inside the Earth’s crust is called Earthquake.

  • Major earthquakes are much less frequent.
  • There can be a great loss of life and property due to Earthquakes.
  • Earthquakes can cause fires, floods, landslides and tsunamis.
  • Examples of major earthquakes in India 
  1. On 8 October 2005, a devastating earthquake affected in Uri and Tangdhar towns of North Kashmir.
  2. Before that, a major earthquake occurred on 26 January 2001 in Bhuj district of Gujarat.
Class 8 Science Chapter 12: Some Natural Phenomena: Earthquake

Also Read:- Diploma in Fire and Safety: Courses, Fees, Salary, Jobs and Scope

Structure of Earth

Earth consists of 4 zones: Crust, Mantle, Outer Core, and Inner Core.

  • The outermost layer of the earth i.e. the crust, is not in one piece. It is fragmented. Each fragment is called a plate.
  • These plates are in continuous motion. So, when these plates either brush against each other or collide with one another, they cause disturbance and tremors in the Earth’s crust.
  • Tremors on the earth can also be caused when a volcano erupts, a meteor hits the earth, or an underground nuclear explosion is carried out. However, most earthquakes are caused by the movement of the Earth’s plates.
  • The boundaries of the plates that are the weak zones where earthquakes are more likely to occur are known as seismic or fault zones.
  • In India, the areas most threatened are Kashmir, the Western and Central Himalayas, the whole of North-East, Rann of Kutch, Rajasthan and the Indo–Gangetic Plain. Some areas of South India also fall in the danger zone.
  • Destructive earthquakes have magnitudes higher than 7 on the Richter scale.
  • The tremors produce waves on the surface of the earth. These are called seismic waves. The waves are recorded by an instrument called the seismograph.
Class 8 Science Chapter 12: Some Natural Phenomena: Structure of Earth

Protection against Earthquakes

We must take necessary precautions to protect ourselves all the time. Here are some protective measures against earthquakes:

  • All the buildings should be so designed that they can withstand major tremors.
  • In highly seismic areas, the use of mud or timber is better than using heavy construction material.
  • Keep roofs as light as possible.
  • It is better if the cupboards and shelves are fixed to the walls so that they do not fall easily.
  • Be careful where you hang wall clocks, photo-frames, water heaters etc., so that in the event of an earthquake, they do not fall on people.
  • Since some buildings may catch fire due to an earthquake, it is necessary that all buildings, especially tall buildings, have fire fighting equipment in working order.

If you are at home:-

  • Stay away from tall and heavy objects that may fall on you.
  • Don’t use lifts during an Earthquake.
  • Take shelter under a table and stay there till the shaking stops.
  • Turn off the gas pipeline. 
  • If you are in bed, do not get up. Protect your head with a pillow.

If you are outdoors:-

  •  Find a clear spot, away from buildings, trees and overhead power lines. Drop to the ground.
  • If you are in a car or a bus, do not come out. Ask the driver to drive slowly to a clear spot. Do not come out till the tremors stop.

Important Definitions in NCERT Class 8 Science Chapter 12: Some Natural Phenomena

Some important definitions covered in the chapter are mentioned below:-

  • Electroscope: An electroscope is a device used to detect whether an object is carrying a charge.
  • Earthing: The process of transferring charge from a charged object to the earth is called Earthing.
  • Earthquake: The sudden shaking and trembling of the Earth due to the disturbance deep inside the Earth’s crust is called Earthquake.
  • Fault zones: The boundaries of the plates that are the weak zones where earthquakes are more likely to occur are known as seismic or fault zones. 
  • Seismograph: The tremors produce waves on the surface of the earth. These are called seismic waves. The waves are recorded by an instrument called the seismograph.
Chapter 1Chapter 2Chapter 3
Chapter 4Chapter 5Chapter 6
Chapter 7Chapter 8Chapter 9
Chapter 10Chapter 11Chapter 12
Chapter 13

NCERT Solutions of Class 8 Science Chapter 12: Some Natural Phenomena

Let us now explore solutions to NCERT Class 8 Science Chapter 12 questions. Get answers to all writing questions in the lesson ‘Some Natural Phenomena’ to understand the lesson and ace your Science exams.

Exercise Questions

Select the correct option in Questions 1 and 2.

1. Which of the following cannot be charged easily by friction?

(a) A plastic scale

(b) A copper rod

(c) An inflated balloon

(d) A woollen cloth.

Soln:

(b) A copper rod.

2. When a glass rod is rubbed with a piece of silk cloth, the rod

(a) and the cloth both acquire a positive charge.

(b) becomes positively charged while the cloth has a negative charge.

(c) and the cloth both acquire a negative charge.

(d) becomes negatively charged while the cloth has a positive charge.

Soln:

(b) becomes positively charged while the cloth has a negative charge.

3. Write T against true and F against false in the following statements.

(a) Like charges attract each other. (T/F)

(b) A charged glass rod attracts a charged plastic straw. (T/F)

(c) Lightning conductors cannot protect a building from lightning. (T/F)

(d) Earthquakes can be predicted in advance. (T/F)

Soln:

a) False 

b) True

c) False

d) False

4. Sometimes, a crackling sound is heard while taking off a sweater during winter. Explain.

Soln:

The sweater is made up of wool. When we take it off, it becomes charged due to the friction between the sweater and the body. This causes the crackling sound.

5. Explain why a charged body loses its charge if we touch it with our hand.

Soln:

When we touch a charged body, the charge, through our body, gets conducted to the Earth. Hence, the charged body loses its charge.

6. 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?

Soln:

The destructive energy of the Earthquake is measured on a device known as the Richter Scale. It has a reading from 1 to 10.

Yes, an Earthquake measuring 3 on the Richter Scale would be recorded by a seismograph.

No, an Earthquake of such magnitude would not cause much damage. Earthquakes of reading 5 and above are more severe. 

7. Suggest three measures to protect ourselves from lightning.

Soln:

  1. On hearing the sound of lightning, we should rush to a safer place. A house or a building is a safe place. If you are travelling by car or by bus, you are safe inside with windows and doors of the vehicle shut.
  2. Don’t carry an umbrella during a thunderstorm as it may conduct the electricity to you.
  3. In an open field, squat low on the ground. Place your hands on your knees with your head between the hands. This position will make you the smallest target to be struck.

8. Explain why a charged balloon is repelled by another charged balloon, whereas an uncharged balloon is attracted by another charged balloon.

Soln:

The charged balloons carry a similar charge, hence they repel each other. When a charged balloon is brought close to an uncharged balloon, then the uncharged balloon acquires a charge opposite to that of a charged balloon by the induction of charge. Hence, it gets attracted towards the charged balloon. 

10. List three states in India where earthquakes are more likely to strike.

Soln:

Assam, Gujarat, and Jammu & Kashmir are the three states where Earthquakes are more likely to occur.

11. Suppose you are outside your home, and an earthquake strikes. What precautions would you take to protect yourself?

Soln:

If you are at home when an Earthquake strikes:-

  • Stay away from tall and heavy objects that may fall on you.
  • Don’t use lifts during an Earthquake.
  • Take shelter under a table and stay there till the shaking stops.
  • Turn off the gas pipeline. 
  • If you are in bed, do not get up. Protect your head with a pillow.

12. The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.

Soln:

No, I would not carry an umbrella in such a weather condition because during a thunderstorm, lightning happens a lot, so the umbrella having a metal rod, may conduct that electricity and give the user a severe shock. 

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FAQs

Q 1. Is Rainbow a natural phenomenon?

Ans: Yes, a rainbow is formed by a natural phenomenon involving the dispersion of light. 

Q2. What is thunder in NCERT Class 8 Science Chapter 12?

Ans: When lightning happens by electric discharge, it is accompanied by sound. That is known as thunder. 

Q3. Can you touch a rainbow?

Ans: A rainbow is formed due to the dispersion of light through the raindrops. It is not a solid thing, it is just light. So we cannot touch the rainbow.

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