CBSE Class 8 Physics Notes for Chapter 5 Some Natural Phenomena

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           CHAPTER 5 SOME NATURAL PHENOMENA
 
 
CHARGING BY RUBBING
When some objects, like a glass rod and a silk cloth, are rubbed against each other, they acquire a small charge. These objects are called charged objects.
 
TYPES OF CHARGES AND THEIR INTERACTION
Like charges repel and opposite charges attract each other.
The charge acquired by a glass rod when it is rubbed with a silk cloth is considered as positive.
 
ELECTROSCOPE
A device used to test whether an object is charged or not is called an electroscope.
 
DISCHARGING AND EARTHING
When a charged body loses its charge from coming into contact with a conductor and transferring its excess charge, it is said to become discharged. This process is called discharging.
When the charge on the charged body gets transferred to the earth, it is called earthing.
 
LIGHTNING
Lightning, in simple terms, is an electric spark on a large scale. Lightning is caused by the accumulation of charges in clouds.
The vigorous movement of winds during thunderstorms separates the charges. The positive charges collect near the upper edges of the clouds and the negative charges collect near the lower edges. There is a collection of positive charges near the ground as well. When these negative and positive charges meet, bright light and loud sound is produced. This bright light is lightning. And this process is called electric discharge. This electric discharge can occur between two clouds or between clouds and earth.
 
LIGHTNING CONDUCTORS
A lightning conductor is used to protect buildings from lightning. A metallic rod which is taller than the building is installed. One end of the rod is kept out in the air. The other end is buried in the earth. This rod provides a route for the transfer of electric charge to the ground.
 
EARTHQUAKE
An earthquake is a sudden shaking or trembling of the earth due to the movement of tectonic plates. The boundaries of the plates are the weak zones where an earthquake is more likely to occur. These zones are called seismic or fault zones.
The strength of an earthquake is measured on a Richter scale.
 

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