The chennai floods and the devastation they've caused have marred the beauty of the rains for me . Well, that's a whole long story, and a story for another time. For now, the electrifying lightning is the centre of our discussion. What do we know about it? How does it occur? Why does lightning happen? How dangerous is it ?
Before we get further into lightning, have you guys ever seen these scenarios? You comb your hair
with a plastic comb and see your hair standing at the end? You just remove your sweater and you see tiny sparks. You walk on a carpet barefoot and when you touch the door knob you kinda get a small shock and you withdraw your hand immediately. In the morning, when you get up after a peaceful night's sleep snuggled under your cozy blanket, you see tiny sparks when you remove your blanket. If you need to explain this is to your kiddo, perform the famous plastic comb attracts paper bits experiment. Shred paper into tiny bits. Take a plastic comb and run it through your hair or rub it against woollen sweater/sock several times. Now bring the plastic comb near the paper bits. You will find the paper bits sticking to the comb for a brief moment. All these are small scale versions of the lightning. Similar phenomena, but lightning is very large scale.
One other thing we need to know about is the cloud. What are they made up of and how are they formed ? They are made up of tiny water particles. Water vapor is found in the air around us. As the water vapor rises into the atmosphere, it cools down into tiny water droplets and sticks onto the dust particles, ice or whatever small particles are present there, thus forming a cloud. These tiny particles of ice keep moving and rub against each other constantly. And when they do that, they rub off charge against one another. Just like the hair and the comb, these particles split up into positively charged particles and negatively charged particles. And the positively charged being lighter rise up towards the top of the cloud and the negatively charged particles towards the bottom of the cloud.
When these charges go on accumulating, and when the difference is wider, the electrons flow from the negatively charged side to the positively charged side to ease out the inequality, thus forming lightning. This is intra cloud lightning. Similarly lightning can happen between two different clouds. Another scenario being between the cloud and the earth. The most dangerous form. It can cause real havoc at the site of incidence. The bottom of the cloud being negatively charged, repels electrons from the surface of the earth or anything that's jutting out of the earth. Thereby making that part positively charged. And eventually, electrons flow from the bottom of the cloud to the nearest positively charged part on the earth. And the taller the building or the structure, the higher the risk of lightning strike.
And these electrons while in transit, get so excited, when they return to their normal state they give out the energy in the form of light. And that's the lightning we see. The energy of the lightning is so huge that it rapidly heats the air through which it travels. The heat causes rapid expansion in the air leading to the monstrous thunder we hear.
That being lightning, what can we do to stay safe ? We have lightning conductors that are placed on tall buildings to safely conduct the huge amount of electricity from the lightning into the earth, thereby avoiding the damage from it. Never stay near the trees during a storm. Try and switch off electric equipment during the storm. And if you see your hair standing straight during storm, meaning your hair is positively charged and you are at a risk of being a victim of a strike. Stay safe. Apparently, staying inside a car, without being in contact with the metal exterior can keep you safe. And that that acts like a faraday cage and could keep lightning away.
Now, isn't that a new term. Faraday cage!
Just before learning about Faraday cage, let me pose another question. We understand that lightning happens when electrons flow from where they are abundant to a place where there is less of them. So potentially anything that is charged is at a risk. And the charges in the cloud come from constant rubbing or bumping of the tiny ice particles in the atmosphere, we said. What about a plane that flies high up in the air and happens to constantly rub against the particles in the air, or the cloud? Doesn't it sound like it is more susceptible to a lightning strike? Imagine how that would be... (God forbid .. touch wood and all the other good luck charms) Have you even given this a thought? How is the aeroplane protected?
However, in the unlikely event that the strike happens, the plane uses its other line of defence. It's aluminium body. The body acts as a good conductor and keeps the charge off the interior. There we are, that's what a faraday cage is. It keeps the charge on the exterior alone and shields the interior. So we are safe. Phew! A renowned scientist called faraday, conducted an experiment where he lined the exterior of the room with metal and passed current through it and proved that while the exterior is carrying the surge of electrons the interior is unaffected.
How does that work? I found a simple explanation from wikipedia.
"Animation showing how a Faraday cage (box) works. When an external electrical field (arrows) is applied, the electrons (little balls) in the metal move to the left side of the cage, giving it a negative charge, while the remaining unbalanced charge of the nuclei give the right side a positive charge. These induced charges create an opposing electric field that cancels the external electric field throughout the box."
"Animation showing how a Faraday cage (box) works. When an external electrical field (arrows) is applied, the electrons (little balls) in the metal move to the left side of the cage, giving it a negative charge, while the remaining unbalanced charge of the nuclei give the right side a positive charge. These induced charges create an opposing electric field that cancels the external electric field throughout the box."
So the car is a faraday cage. Protects you from lightning. The plane is. New concept, but looks like its all around us right? Let's think of more examples to help you relate to it. Remember sometimes when we are in a lift, our phone conversation gets disrupted because of the loss of signal. I know what you are thinking. Cellphones don't use electricity to communicate. It uses radio signals. Absolutely. These radio signals are some form of electromagnetic radiation and the faraday cage tries its utmost to protect the interior from electromagnetic radiation.
If you are wondering what this new term 'electromagnetic radiation' is .. I'm going to break it up into tiny bits of essential information just enough to understand this article. Electromagnetic radiation has three terms : electro, magnetic and radiation. Remember, electric field and magnetic are inter related and one causes the other and vice versa. Radiation is the energy that is emitted out. To put it simple, energy released when certain electrical charges interact. UVrays , visible spectrum, IR, radio waves, gamma waves, X rays all are part of the electromagnetic spectrum. All waves. All have energy, length and frequency.That said, the faraday cage protects the interior from electromagnetic radiation.
Oh dear. Too technical isn't it? Let's deviate a tiny little bit and talk about something eerie. Yes, you heard it right, I did say eerie. We are going to talk about ghosts now. Spooky!! Do you guyz watch horror movies? That's one genre I honestly keep myself away from. Anyways, I happened to see one episode of a very popular television series called 'castle' where they investigate a murder of a ghost hunter. ( You guys wouldn't believe this .. but as of now, as I'm writing about this spooky subject, my lappy screen just turned on and off and the CD drive just automatically ejected the CD !!!) Hmmm.... back .. to .. the ... castle episode. So, while investigating they learn that ghost hunters use ElectroMagneticField Meter. It's a device that measures abnormal paranormal activity. ( God! I wish I had that with me now!! ) That's one new term and concept I learnt the other day. Ghosts are or cause some sort of electromagnetic radiation. And that would mean ..... a Faraday cage can technically trap ghosts??? Wow.. what a thought! One other day, I saw yet another episode of yet another popular television series Doctor Who ( Yes, I do watch a lot of these series, but hey, look how informative they are !) , where they showed us exactly the same thing. Faraday cage and ghosts getting trapped in them. What an innovative use of a faraday cage that would be huh...
Some other uses of faraday cage : Electrical linemen wear faraday suit to protect them from electric shock. MRI room in a hospital is designed as a faraday cage to minimize interference from outside. Sometimes, high profile equipments are kept in a faraday cage to protect them from EMP, Electromagnetic Pulse. ( EMP destroys every electrical equipment in the vicinity.) How very handy.
That was about faraday cage. Now back to lightning. Have you ever wondered why lightning is never depicted as a straight line, and why it has a zigzag or a jagged shape? I read from the internet that lightning happens in many small steps. That is, when the bottom of the thundercloud assumes negative charge, the electrons take a leap, the first leap. Apparently, this first leap is only a few hundred metres long. Then, from the botoom of that leap, another leap happens and so on. Similary, the ground which had assumed a positive charge, sends its positive charge up in leaps and in steps. Now each of these steps are independent of each other and they chose their path of least resistance. Which is why lightning is zigzag.
Early men used to think of Lightning as a warning or punishment from God. We still do have that mythological stories talking about lightning as Indra's weapon Vajra, and as Zeus's weapon thunderbolt according to the Greeks. But that was back then, when we had no knowledge of the science behind lightning. I hope this post has bestowed upon you the lightning enlightenment. ( Is my heading justified now! Phew! )
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