Learn about lightning - the deadly beauty of nature

Lightning is one of the extremely beautiful natural phenomena. But it is a 'deadly' beauty. With temperatures higher than the solar surface temperature, and electrical impulses in all directions, lightning becomes one of the interesting research objects of physicists.

In the face of such great beauty and strength, a question arises: How is lightning formed? Most of us know, lightning emerges from the cloud of electricity, but the specific mechanism, not everyone knows. In this article, let's work together to see how lightning is born.

This process is quite complicated, but can be summarized as follows:

- Starting with the water cycle. Water will evaporate when receiving heat from sunlight, soaring, cold, condensing into millions of small droplets, then we will see clouds on the sky.

- The process of evaporation and condensation occurs continuously, the water vapor and small droplets in the clouds will interact with each other, plus the freezing phenomenon, will make the difference of charge: positive charge in the upper part of the cloud, while the negative charge is on the bottom.

- The formation of two areas of opposite charge also generates the electric field. The greater the charge difference, the stronger the electric field.

- A strong electric field, to a certain extent, will cause the surrounding air to be ionized, allowing an electric current to be transmitted through this ionized air area (the plasma itself) easily. This transmission path, also known as the step leader.

- At the same time, the Earth's surface will be affected by a negative electric field beneath the clouds, and Earth-based objects (including humans) will lose electrons and positively charge positively.

- When the leader steps to the surface of the Earth, it will form a complete path leading from the clouds to the ground. And at that moment, a lightning strike came down.

- The air around the lightning bolt will be strongly heated, stretching abruptly, and the sound of thunder immediately follows - thunder.

And here are the details of the lightning formation stages.

It all comes from a familiar phenomenon: the water cycle. To better understand, let's talk a little bit about evaporation and condensation.

Evaporation is the phenomenon of a liquid absorbs heat, and changes to a vapor. Can take a simple example, the puddles after a while of rain will disappear, or laundry finished drying clothes will dry . all that is evaporation. Because water will absorb heat from sunlight, water molecules will move faster, and at some point, they will separate from the liquid solution to fly into the air. Gradually, all that water will fly into the air into steam.

Condensation - condensation - is a process of gas loss or heat loss, and returns to liquid form. You all know that heat is transmitted from high temperature to low temperature. When the steam rises, the atmospheric temperature above is much lower than the surface of the Earth. So when the steam rises, the temperature is colder, they lose heat, concentrate, and return to their original liquid.

Now we return to the water cycle. Water and moisture on the Earth's surface absorb heat from sunlight, water molecules start to separate from the liquid and turn into a vapor. The steam rises high, the lower the temperature, the lower the steam, and condenses into droplets. Earth's gravity pulls them down, and forms rain. And so on, the water cycle repeats. Also, when the high temperature is cold enough, it will condense the steam faster, freeze and form snowflakes, then, instead of rain, it will snow.

You may be wondering, what is the water cycle here? In fact, it has a very important role in forming lightning. The next part, will talk about 'electric storm'.

Electrical storm - electrical storm

In an electrical storm, clouds are charged, like a giant capacitor in the sky. The upper part of the cloud is positively charged, and the lower part is negatively charged. So, why form such a charge difference? This issue is still very controversial, however, below is an accepted assumption.

In the water cycle, water vapor is condensed in the atmosphere, and the image we see of this process, are clouds. The cloud is a collection of many drops of water, and rocks too. When the process of evaporation and condensation occurs continuously, there is an interaction between water vapor and water droplets or snowflakes in the cloud, even drops of water are falling on Earth. This interaction, usually occurs on the lower floor below the clouds. The important point is that, this collision separates the electrons in the rising steam.

And so, the process of electron separation occurs in the lower part of the cloud, so this region is negatively charged. In contrast, water vapor - which carries a positive charge due to the loss of electrons - continues to evaporate, soaring above, through clouds, so the area on the cloud will be positively charged. Interaction between elements, along with the freezing phenomenon, is a reasonable explanation for the formation of charge differentials - conditions needed to form lightning strikes.

When there is a charge difference in the clouds, the corresponding electric field will appear: the lower negative electric field and the upper positive electric field. The strength of the electric field is directly related to the amount of charge generated. When continuous interaction and freezing occurs, the electric field gets stronger and stronger over time, and the more powerful the electrons on the Earth's surface will go deeper into the Earth because they interact with the electric field. the negative part of the cloud is low, and therefore, the Earth's surface will be positively charged.

So there is a negative charge area, and a positive charge region, now only needs a pathway for the negative charge region under the cloud to contact the positive charge area on the Earth's surface. The fact is, just a very strong electric field, is enough to make this transmission path.

The ionization process of air

With extremely strong electric fields around clouds (about 10,000 volts / inch), the air starts to break down. Atoms in the air begin to be separated into positive ions and electrons - the air has been ionized. Remember, the ionization process does not increase the charge difference by generating positive electrons and ions; but it only makes the electrons and atomic nuclei apart from each other, essentially in an atom.

And then, electrons will be easier to move than before, because the binding of positive charges at the nucleus is reduced. Ionized air - or plasma environment - is much better at conducting electricity, its electrical conductivity is similar to metal. And, inadvertently, ionized air becomes an electrical conductor to help neutralize the charge difference, as an environment for electric discharge.

After ionizing the air, the path between the clouds and the ground is formed. Next, will be the step leader.

Step leaders

After ionization occurs, and the plasma environment forms, the pathway does not form immediately, but is ionized air, not at the same time. They are collectively called steps leaders.

Another problem, the ionized air is irregular, there is a stronger ionized region, there is a weaker area. Dust and dirt make ionized air stronger. In addition, the shape of the electric field also plays no small role: it depends on the area of ​​charged particles. If the electric field is parallel to the ground, and it is small enough to consider the curvature of the Earth's surface to be negligible, then this is like two plates of parallel capacitors.

Ok, so now, we have a cloud of electricity, with the step leaders stretching from the cloud to the ground. These leaders, with a slight reddish tinge, are faint. Once formed, the leader will exist until the current is fired, not related to the leader's position. The leaders have two possibilities: one is to continue to develop more broadly into layers, corresponding to the extent of expansion of the ionized air area, the second is to remain in the state of plasma until the current passes. .

And when the leader finally reached the ground, the path between the cloud and the ground was formed. Remember, the leader is not a lightning strike, it's just a way to help lightning. Lightning is a large electrode flowing from the cloud to the ground.

Positive charge range and air expansion

When the step leaders approached the ground, everything on the surface of the Earth began responding to a strong electric field: things began to positively charge and formed a positive-positive streamer. These streamer also have a light purple color and appear more clearly on the sharp edges of the objects. The human body is also capable of forming positively charged streamer when standing in a strong electric field, such as the electric field of storm clouds. Once formed, the streamer does not directly connect to the negatively charged area in the clouds, but the leaders themselves will be responsible for the transmission and formation of the path.

And what must come will come, step leader will meet the streamer. A special thing, the streamer contacting the leader step is not necessarily the streamer of the object closest to the cloud, such as tall trees or poles . Lightning often hits the ground, even if there are objects around it much higher.

After the step leader and the streamer come into contact, the path passed by the ionization of the air is completely formed from the cloud to the ground. Once the path is complete, there will be a strong electric current moving through it to neutralize the charge difference between the ground and the cloud. The light that we see - lightning - is an effect of that current.

When an electric current is present, it is at the same time an extremely high temperature around the area where the current passes. The amount of heat generated is extremely large, with temperatures even higher than the temperature on the Sun's surface. The surrounding air was heated, suddenly expanding, and I heard thunder - thunder.

Thunder is a wave of waves emanating from the path of lightning, due to warming of air and sudden expansion. This expansion is also a form of sound waves. The sound of thunder is not harmless: if it is close enough, you can feel the sound waves impacting your body. It is like exploding an atom bomb: most of the destructive power of the explosion is due to the energy of the impulse transmitted through the air. In fact, shock waves generated by lightning strikes can destroy buildings and harm human bodies. You will see better if you stand near the lightning, and the energy of the pulse will decrease with distance. Also, as you know, the sound moves a lot slower than light, so you will hear thunder after seeing lightning for a few seconds.

Multiple strike

If you notice, you will see, when lightning strikes, there will be many smaller branches emanating from the main lightning. And the main lightning, after hitting down, will not lose immediately, but will fade.

When the first bolt hits, the current moves to neutralize the charge difference. In order to neutralize the whole, it is necessary to have the current from the other leader steps also have to launch to the ground. The electrons in the step leaders are free to move, follow the leader to go to where the main lightning strikes down. After the first blow, it will often involve secondary attacks. Later strikes still follow the path of the main shot, but the surrounding step leaders do not play any role in this discharge.

In nature, what we see is not necessarily the same as we think. And so are these secondary blows. Usually, a key shot will take around 30-40 extra shots. Based on the extremely short delay between lightning strikes, the first lightning image can be observed longer, and fading. In fact, it was because the secondary lightning strikes occurred immediately after the first hit broke out, making us mistakenly believe that it was due to the first long-hitting strike. And similarly, the secondary hits made them look like the first hit was flashing.

And, that's all the complicated mechanisms for forming a lightning strike. It was as complicated as that, but it all happened in a split second, less than a second. Cameras capable of taking photos in a short time can capture images of positively charged streamer. If you want to see this phenomenon yourself safely, make a Van de Graaff transmitter, and run it in a closed room. As you approach the machine, your fingers will also emit a pale purple color, like step leaders or positively charged streamer.

Lightning rod

The lightning rod was first built by Benjamin Franklin. The construction of a lightning rod is quite simple: a metal rod is mounted on the roof, about 2cm in diameter. It is connected to many copper or aluminum wires, similar in diameter, directly connected to the ground.

The purpose of the lightning rod is often misunderstood. Many people think that lightning rod is to "attract" lightning. In fact, it would be more accurate to say that the lightning rod creates a low-resistance path to the ground, to help guide extremely large currents from downward lightning strikes safely to the ground. Materials for lightning rod and conductor require good electrical conductivity, otherwise, with the energy of lightning, they will heat up very quickly and be damaged immediately.

Lightning can 'bounce around' when it hits. Where it jumps, it depends on that region's resistance: the smaller the resistor, the more likely it is that lightning will strike. When lightning strikes near the lightning rod, with very low resistance of the lightning rod, lightning will tend to hit it and not cause harm to the surrounding objects. And as mentioned above, lightning rods do not "attract" lightning, do not strike more lightning, but it only helps 'direct' lightning. Whether or not there is a lightning rod system, lightning still strikes like that.

Lightning: threat

More than 1000 people are struck by lightning every year in the US, and more than 100 of them die. So, don't joke with lightning.

If you are going out on the street and suddenly a thunderstorm rises, thunder rumbles, find shelter now. Don't try to go on - you will become a mobile lightning rod. Go into the house, or stay in your car. Oh, why can cars help you avoid lightning? Because, lightning will move on the surface of the car directly to the ground; it is like a Faraday cage: a metal cage will protect objects inside it from external currents, because electricity will run on the surface of the cage and lead to the ground. Never stand under a tree during stormy weather: the tree is also a lightning absorber like a lightning rod. Keep your legs together, bend down to the fullest extent and contact the ground as little as possible.

Never lie on the ground - when lightning strikes the ground, the electromagnetic current will radiate in all directions, and if it passes through you it will be very dangerous. You can stop your heart immediately. So, if you still want to go out in stormy weather, go as low as possible, and contact the ground as little as possible.

If you are indoors and want to call someone, use a cell phone, or any wireless phone. If lightning strikes the phone line, electricity will follow the line and endanger the users of wired phones.

And finally, be careful with your home plumbing, especially when your home uses metal pipes. Commonly used PVC (polyvinyl chloride) pipes will reduce the conductivity of lightning. But if you're not sure which tube you use, be patient when the storm passes.