Class 8 Science

Lightning

Lightning is observed as a bright streak of light during a thunderstorm. Lightning is always accompanied by the sound of thunder. The transfer of charge from clouds to the earth or from cloud to cloud is called lightning. In simple words; lightning is an electric spark which happens on a grand scale in the sky.

Mechanism of Lightning

  • During a thunderstorm, the air currents move upward and water droplets move downward. These movements take at very fast pace and it results in separation of charges in the clouds.
  • The positive charges accumulate at the upper edges of the clouds and the negative charges accumulate at the lower edges of the clouds. Scientists are yet to understand the exact reason for this.
  • At the same time, the ground becomes positively charged.


Air is a bad conductor of electricity under normal circumstances. But when the amount of charge becomes too much in the clouds, the air is not in a position to hold on to this charge. As a result, the electric charge is transferred to the ground. This appears like a bright streak of light across the sky; which lasts for a few seconds.

mechanism of lightning

Dangers of Lightning:

Lightning can damage houses and trees. It can also kill people and cattle. Sometimes, lightning can main a person for life.

Safety During Lightning:

  • No open place is safe during lightning and hence a home or any other building is the safest place during lightning.
  • The first sound of thunder is like a warning call for lightning. Hence, one should rush to a building soon after hearing a sound of thunder. One should come out of home only a few minutes after the last sound of thunder.
  • You should not carry an umbrella (with a metallic handle) during thunderstorm. Metallic handle can be a potential target for lightning.
  • Tall trees and other tall structures are more prone to be hit by lightning. If you are caught in the open, try to hide under a short tree.
  • If you are in open and have no place to hide, then crouch on the ground and keep your head between your knees and hands.
  • Don’t take shower during lightning.
  • Use of phone should be avoided during lightning.
  • Television should be disconnected from the antenna.
  • Avoid operating the electric switches during lightning.


Lightning Conductor:

This is a simple device which protects a building from being hit by lightning. It is composed of a vertical metallic rod which usually has a trident at the top. The base of the metallic rod is attached to thick metallic wire; which goes very deep inside the earth. This metallic wire provides a passage for earthing.

When lightning strikes, electric charge goes to the lightning conductor and it then goes to earth. Thus, a lightning conductor helps in preventing any damage to the building.

Earthquake

Sudden shaking of the earth; which lasts for a very short duration is called earthquake.

Tectonic Plates: The crust of the earth is composed of several pieces of landmass. These are called tectonic plates. The tectonic plates are in continuous motion. They keep on brushing against each other or striking each other. When a tectonic plate brushes against another or strikes another tectonic plate; it results in vibrations in the tectonic plates. These vibrations are experienced by us in the form of an earthquake.

tectonic plates

Seismic or Fault Zones: The boundaries of the tectonic plates are at high risk of earthquake. These boundaries are called seismic zones or fault zones. In India; Kashmir, western and central Himalayas, the whole of the north-east, Runn of Kutch, Rajasthan and Indo-Gangetic Plain are at high risk of getting hit by an earthquake. Some parts of the Deccan Plateau are under the seismic zone.

Seismograph: Seismograph is a device which records the seismic activities. It is composed of an oscillator, writing device and a roll of paper. The writing device is attached to the oscillator. In case of an earthquake, the oscillator begins to oscillate. This creates oscillation in the writing device; which plots wave-like patterns on the paper. The wave-like pattern is then analysed by seismologist to interpret the various features of an earthquake.


Richter Scale: The Richter Scale was developed in 1935 by Charles Richter and Beno Gutenberg of California Institute of Technology. This is a logarithmic scale which shows the intensity of an earthquake. The intensity of an earthquake is measured on a scale of zero to 10. But earthquakes of more than 9 Richter have never been reported. The magnitude of earthquake increases by 100 times when we move one point on the Richter scale. This means that an earthquake measuring 5 on Richter scale is 100 times more powerful than one measuring 4 on Richter scale.

Most of the earthquakes go unnoticed by us because they are below 4 on Richter Scale. Earthquakes which measure more than 7.5 on the Richter scale can be highly damaging.

Dangers Due to Earthquake

An earthquake cannot cause any damage on its own. Most of the damages caused by an earthquake are because of collapse of man-made structures; like buildings, bridges, poles, etc. Sometimes, an earthquake can result in tsunami which causes large scale damage. The infamous tsunami in the Indian Ocean which came on 26th December 2004 was because of a massive earthquake near Java.

Protection Against Earthquake:

It is impossible to predict an earthquake and hence we need to take several precautionary measures to avoid or minimize the damage which may happen because of earthquake. Some of the preventive measures are as follows:

  • Buildings should be made quake proof. Engineers and architects are the experts who can give suitable advice in this regard.
  • Light-weight materials should be used for making the buildings in earthquake prone areas.
  • Cupboards should be fixed to the walls so that they do not fall on someone during an earthquake.
  • People should be made to practice drills for earthquake. Such drills should be frequently organized in schools and at public places.
  • In case of an earthquake, you should hide under a table or any other similar structure. If you are in bed, then keep a pillow over your head and do not move out of the bed. If you are in an open area, try to move away from buildings and other structures.
  • Proper installation of fire-fighting equipments should be ensured in buildings. Fire due to short circuit and gas leakage is quite common during an earthquake.