Lightning

Lightning

We have seen bright, striking lights in the dark sky during the rainy season. It is as dangerous as it looks bright in the sky. What causes this phenomenon of lightning to occur during the storm? Even though the exact science behind the concept of lightning is not well established, let's deal with the most accepted models of lightning.

 

Lightning

Natural Capacitor:

Let's go from the basic concepts of electrostatics that we learned in classes 11 and 12. Lightning can be visualized as the electrical breakdown of a natural capacitor formed between the Earth's cloud and the ground, with the atmosphere as a dielectric medium. What is a capacitor? A capacitor in electronics is used to store energy in the form of electrostatic fields in them. A simple capacitor can simply be treated as two large plates of equal size containing charges of opposite magnitude separated by a small distance. So basically, the capacitance value of the capacitor can be found using the dimensions of the plates, the distance between them, and the nature of the medium filled inside the gap between the plates. Whenever the capacitor is connected to the circuit, the current that flows from the battery charges the capacitor by building charges in them, eventually creating an electric field between them. But, however, there is still a limit for any capacitor to hold a specific amount of charges between them; once the potential difference between the plates goes beyond the breakdown voltage, the capacitor breaks down, creating sparks between the gaps. How can we relate this to the lightning effect? Assume the cloud and the ground to act as two plates of capacitors and the atmosphere as the dielectric medium between them. When a sufficient number of negative charges accumulate on the cloud, it induces the positive charges on the ground, and it starts developing the electric field between them. When this value of the electric field between them goes beyond the breakdown limit, the capacitor breaks down and lightning flashes.

Q. Lightning can be considered a phenomenon caused by the breakdown of a natural capacitor. When an electric field of strength 41 G V m develops between the ground and the cloud. Find the power delivered by the lightning caused by breakdown at this stage if the natural capacitance is 14 nF. Assume the breakdown took just 0.2 seconds.

 

The energy of the capacitance formula learned in class 12 is given by E = 0.5*C*(V2). By using this formula, the energy stored in the capacitor is 1.17 e13 J. If this amount of energy is delivered in the form of lightning due to the breakdown time of 0.2 seconds, the power is calculated as P = E/t, so the power delivered is around 5.85 e13 watts, which, when passed directly inside a human body, makes him completely dead. Note: The numbers used here are just for a rough calculation to give you an idea of the power of the lightning effect. You can now calculate the current carried by the lightning in the above question if the distance between the cloud and the ground is given as 820 m. Again, note that these numbers that we get do not correspond exactly to real-life values.

Lightning leader:

In the previous section, we dealt with the fact that the clouds get negatively charged, and this induces positive charges on the ground, making it possible for the electric discharge to happen between them during the breakdown. But how are these charges made? Whenever new water droplets get formed and rise above, they rub with the cloud, and friction between them causes the charge separation to happen between the clouds; the lower part of the cloud is negatively charged and the upper part is positively charged. This lower part of the cloud that faces the ground induces a positive charge on the ground, creating an electric field between them. Initially, there is a formation of stepped leaders, which is basically the path of ionized gas in which the neutral atoms and air get ionized. This path keeps on building from the cloud to the ground, and a similar stepped leader moves from the ground to the top as well. This creates bidirectional stepped leaders moving towards each other. When they come in contact, they complete the channel for the electric discharge to happen, and the lightning flashes, a bright strike of light propagating from the ground to the cloud. As the stepped leader comes down, it gets divided into tree-like branches, making us see that the lightning looks branched. Some people have experienced that their hair sometimes stands straight during a storm, indicating that they are standing in the channel for the lightning to pass. It is safe for you to leave the place as quickly as possible before the lightning strikes you.

One more interesting calculation regarding the calculation of the distance of a thunderstorm from us As soon as you see a lightning strike, start a stopwatch and stop it when you hear the thunder storm sound; basically, calculate the time it takes for you to hear the thunderstorm after the lightning strikes. Now, we know that the speed of light is much faster than the speed of sound; that's why we see the lightning first and hear the thunder storm later because the sound travels at a speed of 340 m/s. So basically, it takes some time for us to reach Now that you have counted the time it took you to hear the sound, multiply it by the speed of sound to know at which place the thunder struck.

 

Q. Rahul witnesses the flash of lightning at t = 0 and hears the thunder at t = 5 seconds. Help him calculate the distance of the thunderstorm from him. The speed of sound in the air at that temperature is 345 m/s.

 

Distance of the storm = speed of sound in the air at that temperature * time taken for him to hear the sound

Distance of the storm = 5 * 345 m

Distance of the storm: 1.725 km

 

It is always safe for you to stay in a safe shelter during lightning.