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NCERT Solutions for Class 8th Science

 

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Chapter 15. Some Natural Phenomena

Chapter Review

 

 

 

Chapter Review:

  • Lightning is caused by the accumulation of charges in the clouds.
  • Lightning is a natural phenomenon which occurs in the sky h clouds sparkwit.
  • This is a device by which it is identified of charge on an object is carrying or not. This device is known as electroscope.
  • The process of transferring of charge from a charged object to the earth is called earthing.

  • When a plastic comb is rubbed with dry hair, it acquires a small charge. These objects are called charged objects.

  • The electrical charges produced by rubbing are called static charges.

  • There are two kinds of charges — positive charge and negative charge.

  • Like charges repel and unlike charges attract each other.

  • Negative and positive charges meet, producing streaks of bright light and sound. The process is called an electric discharge.

  • The disturbance deep down inside the uppermost layer of the earth called the crust.

  • The outermost layer of the earth is not in one piece. It is fragmented. Each fragment is called a plate.

  • The plates are the weak zones where earthquakes are more likely to occur. The weak zones are also known as seismic or fault zones.

  • The power of an earthquake is expressed in terms of a magnitude on a scale called 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.

  • Earthquake is caused by a disturbance deep inside the earth’s crust.

 

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