CBSE Class 8 Science Notes Chapter 15 Some Natural Phenomena
Some Natural Phenomena Class 8 Notes Understanding the Lesson
1. Lightning is an electric spark on a huge scale. It is caused by the accumulation of charges in the clouds.
2. Some objects can be charged by rubbing with other objects. These objects are called charged objects.
3. There are two types of charges – positive and negative.
4. The charge acquired by a glass rod when it is rubbed with silk is called positive.
5. The charge on an ebonite rod when rubbed with fur, wool or flannel is considered as negative.
6. The electric charges generated by rubbing are called static charges.
7. When charges move they constitute an electric current. Thus, moving charges are called current.
8. Like charges repel each other and unlike charges attract each other.
9. A device used to test whether an object is carrying charge or not is called an electroscope.
10. Electric charge can be transferred from a charged object to another through a metal conductor.
11. The process of transferring of charge from a charged object to the earth is called earthing.
12. When a body loses charges to the earth or any other it is said to be discharged.
13. The process of electric discharge between clouds and the earth or between different clouds causes lightning.
14. Lightning strike could destroy life and property. It is, therefore, necessary to take measures to protect ourselves.
15. During lightning and thunderstorm no open place is safe. A house or a building is a safe place. During travelling by car or by bus, it is safe to stay inside with windows and doors of the vehicle shut. Carrying an umbrella is not at all a good idea during thunderstorm. If in a forest, shelter should be taken under shorter trees.
16. Lightning can strike telephone cords, electrical wires and metal pipes. Electrical appliances like computer, TV, etc., should be unplugged. Electrical lights can remain on.
17. Lightning conductor is a device used to protect buildings from the effect of lightning.
18. An earthquake is a sudden shaking or trembling of the earth. It lasts for a very short time. It is caused by a disturbance deep inside the earth’s crust.
19. Earthquake can cause a great loss to our life and property. It can cause immense damage to buildings, bridges, dams and people. It can also cause floods, landslides and tsunamis.
20. Unfortunately, we are not yet able to predict an earthquake accurately.
21. The power of an earthquake is expressed in terms of a magnitude on a scale called the Richter scale.
22. Earthquakes having magnitudes higher than 7 on the Richter scale cause a great destruction to our life and property.
23. Earthquakes are caused by the movement of plates, the boundaries of the plates are the weak zones where earthquakes are more likely to occur. The weak zones are known as seismic or fault zones.
24. We should adopt precautionary and protective measures to save ourselves from the upcoming damages of an earthquake.
Class 8 Science Chapter 15 Notes Important Terms
Crust: The uppermost layer of Earth’s surface (8 km – 32 km) is termed as crust.
Discharge: Discharge is the release or transmission of charges from one object to another through a medium like liquid, gas or solid.
Earth’s plates: The outermost layer of the earth is fragmented. Each fragment is called a plate.
Earthquake: An earthquake is a sudden shaking or trembling of the earth which lasts for a very short time. It is caused by deep disturbances caused by movement of earth’s plates inside the earth’s crust.
Electroscope: It is a device used to test whether an object is charged or not.
Lightning: It is the process of electric discharge between cloud and the earth or between different clouds.
Lightning conductor: It is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed on the roof of elevated structure.
Negative charge: The charge of an object due to excess of electrons is called negative charge.
Positive charge: The charge of an object due to loss of electrons is called positive charge.
Richter scale: The power of an earthquake is expressed in terms of a magnitude on a scale called Richter scale.
Seismograph: It is an instrument which measures and records the magnitude of an earthquake in terms of the shock waves it produces.
Thunder: The loud noise accompanied by lightning is called thunder.
Thunderstorm: A storm accompanied by thunder and lightning is called thunderstorm.
Transfer of charge: Electric charges can be transferred from a charged object to another through a metal conductor.
Tsunami: A sudden violent change in the earth’s surface resulting from a destructive sea wave caused by an earthquake or volcanic eruption is known as tsunami. Coastal areas around the ocean suffer huge Mosses.
Tremor: A small earthquake is called tremor.