15- Some Natural Phenomena | Part 1 | Science | NCERT | Class 8

Hello students, in this blog you can find important summary notes from the Chapter 15, Science , NCERT Book of Class 8. These notes can be used for preparation of various school Competitive Exams, Olympiads and also developing strong Fundamentals.

1. Lightning is also an electric spark, but on a huge scale.

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

3. When amber (a kind of resin) was rubbed with fur, it attracts light objects such as hair.

4. When a plastic refill is rubbed with polythene, it acquires a small electric charge.

5. When a plastic comb is rubbed with dry hair, it acquires a small charge. Such objects like plastic refill and comb are called charged
objects
.

6. During the process of charging the refill and the plastic comb, polythene and hair also get charged.

7. The charges of the same kind repel each other, while charges of different kind attract each other.

8. It is a convention to call the charge acquired by a glass rod when it is rubbed with silk as positive and the other kind of charge is said to be negative.

9. The electrical charges generated by rubbing are static charge.

10. They are called static charge because, they do not move by themselves.

11. When charges move, they constitute an electric current and are not called as static charge.

12. The current in a circuit which makes a bulb glow, or the current that makes a wire hot, is nothing but a motion of charges.

13. Electroscope : A device used to test whether an object is carrying charge or not, is known as electroscope.

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

15. Earthing : The process of transferring of charge from a charged object to the earth is called earthing.

16. Earthing is provided in buildings to protect us from electrical shocks due to any leakage of electrical current.

17. Electric discharge :
• During thunderstorm, there are vigorous movements; i.e. the air currents move upwards and water droplets move downward causing separation of charges.
• The positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges.
• There is accumulation of positive charges near the ground also.
• When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity, is
no longer able to resist their flow.
• Negative and positive charges meet, producing streaks of bright light (called lightning) and sound.

18. The process of electric discharge can occur between two or more clouds, or between clouds and the earth.

19. Lightning strike could destroy life and property and hence it is necessary to take measures to protect ourselves.

20. Lightning Safety :
• During lightning and thunderstorm no open place is safe.
– rush to a safer place.
– move to a safe place only after hearing the last thunder

21. Open vehicles, open fields, tall trees, shelters in parks, elevated places are not safe from lightning strokes.

22. Carrying an umbrella is not safe during thunderstorms.

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2 Comments

  1. Great sir !
    Do keep sending such notes.
    As,We able to get answers at one place.
    😊👍☝️

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