LIGHTNING & THUNDER
Some natural phenomenon of Class 8
LIGHTNING & THUNDER :
Lightning is a giant spark. A single stroke of lightning can heat the air around it to 30,000 degrees Celsius (54,000 degrees Fahrenheit)! This extreme heating causes the air to expand at an explosive rate. The expansion creates a shock wave that turns into a booming sound wave, better known as thunder. This explains why it has the name thunderstorm.
Thunder and lightning occur at roughly the same time, although you see the flash of lightning before you hear the thunder. This is because light travels much faster than sound.
During a thunderstorm, thunder and lightning occur together. But we see a flash of lightning first and hear the number of thunder after few seconds. The time difference that we sense is due to the speed at which sound and light travel. Light travels so quickly (about 300, 000 kilometres in one second) that we see a bright flash of lightning instantly. Sound, on the other hand, travels much more slowly than light- at about 340 m/s through air. Therefore, we can see light in an instant, but it takes a while to hear thunder.
During a storm, wait until we see a flash of lightning, then start to count slowly. For every count of three, the storm is roughly one kilometre away. If we see lightning and hear thunder at just about the same moment, watch out. The storm could be right above us, only a few hundred feet away.
An electric spark is an electric discharge (i.e. flow of electric charges) through air, vacuum or any other gas. We would have seen these sparks at electric switches. Switch off all the lights at night and then observe the switch closely when we switch off the fan switch. We will most likely see a small flash of light. This is an electric spark. This is due to the charges jumping across the small gap formed when the switch is being turned off. Lightning is one example of a huge electric spark in the atmosphere.The flash of light that we see is due to the air molecules being heated up to very high temperatures.
The saying that lightning never strikes the same place twice is wrong. Once the step leader forms the conducting path, charges flow through this path many times, in rapid succession. So lightning strikes again and again at the same place, with intervals of a few tens of a millisecond. It has even struck more than 40 times at the same spot. It is so quick that it is difficult for the eye to detect, but if we observe the lightning very closely, we will notice a brightning and dimming. This is called the 'strobe effect', somewhat like the lights at a disco.
Lightning always follows the easiest path. Lightning strikes buildings or projecting objects such as trees, poles, wires or building than larger, flatter surfaces because the material in them provide easier paths to the ground than the other. The primary target of lightning are lone buildings.
The idea behind the lightning protection is to provide a direct, easy path for the lightning bolt to enter the earth without passing through a building. A lightning conductor runs from the top to the bottom, along the outer wall of the building to be protected. The lower end of the lightning conductor is connected to a metal plate, which is buried deep inside the earth. When a lightning strikes, the lightning conductor provides an easy path for the charge to pass through to the earth, thus protecting the building.
SAFETY MEASURES AGAINST LIGHTNING STRIKES:
Lightning strikes tall buildings and trees. When lightning strikes the earth it can be extremely dangerous. If we caught in thunderstorm then the safety measures to be taken are :
- Do not take shelter under a tree. Even if the tree gets struck by lightning, it could catch fire and cause great harm to us.
- Do take shelter go to indoor.
- We can take shelter inside a car or a bigger vehicle, like a truck.
- We can also sit down in a low-laying place.
- We should not run across a large open field or high ground.
Lightning conductors are used to protect buildings from the damaging effects of lightning