15. Some Natural Phenomena Science class 8 in English Medium ncert book solutions 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.