by Eleftheria Safarika , IB 1-Pierce ACG.
Storms, thunder and lightning are fairly common phenomena which oftentimes scare us, and are sometimes even responsible for natural disasters. However, they are also one of the most prominent and well known manifestations of what we know in physics as electricity.
To understand such electrical phenomena, we should be able to understand the fundamentals of electricity. One basic notion is the one of electric charge. There are two kinds of charge: positive and negative. As it is widely known, like charges repel, while unlike attract. Charge is created when atoms receive or give away electrons. Atoms consist of a nucleus in their center, which is composed by protons and neutrons, the former being a quantum of positive charge, while the others, as their name indicates, are neutral and are not charged. Being a “quantum of positive charge” means they are the smallest quantity of positive charge there can be in nature. Around the nucleus orbit electrons, which are the quanta of negative charge, respectively. Atoms have the same number of protons and electrons, and are thus electrically neutral. When an atom loses or gains more electrons, it becomes charged positively or negatively, and is then called an ion. It is important to stress that electric charge is not created from nothing, nor destroyed. This principle is called conservation of charge. Another idea of electricity is the one of the electric current. The electric current, the flow of electricity, is the oriented motion of negative charges. The electrons are the ones creating the current, because it is they that can leave the atom. There are some materials which make the flow of the electric current easier, while others that hinder it. The first ones are known as good conductors of electricity, or simply conductors, while the others are known as insulators. The conductors contain many electrons that can be put into motion when given energy.
Now let’s get into what happens during a thunderstorm and how lightnings are caused. When thunderous clouds accumulate, it is very probable that lightning will occur. These clouds are charged. Generally, the top part of the cloud has positive charges, while the bottom part has negative charges. It is not yet completely clear to scientists why this division happens. At the same time, because of a phenomenon called charging by induction, positive charges gather on the upper layer of the ground. This way, an electric field is created between the earth and the clouds. An electric field is a vector field created around a charge, which exerts a force to any other charge entering it. Lightning happens when the voltage between earth-clouds gets really high (10s of millions of volts). It may seem that lightning is directed from the clouds to the earth, but in reality, the charges move both ways, meaning both from the clouds to the earth, and from the earth to the clouds. The negative charges on the lower end of the clouds and the positive charges on the upper layer of the ground attract, and slowly some of the negative charges in the cloud start moving downwards, while some of the positive charges of the ground start moving upwards. These negative charges are called step leaders, while the positive ones are called streamers. When the positive and negative charges connect, we see the lightning, and the negative charge of the specific cloud is “emptied” into the ground. During a lightning strike, the intensity of the electric currents reaches at about 50.000 Ampere. However, because of the very small time that it takes for the strike to happen, the energy released from the lightning is not enormous: it is about the same one as the one that a regular lamp would use up in one month.
It’s very easy to calculate how far away a lightning has stricken, just by calculating the time it took the sound to reach us, after we saw the lightning itself. We know that there is a difference between the speed of sound and the speed of light, so it is expected to have this difference between the time we see the lightning bolt and the time we hear the thunder. Light travels with the fastest speed in the universe, 300.000 km/sec, while sound is slower, and travels with a speed of 343 m/sec, which means roughly 1 km in three seconds. Knowing this, it is easy to calculate the distance between us and the place the lightning hit, just by counting the seconds between the shine and the sound. But how is the sound of the thunder created? We know that sound is actually a wave with areas with higher and lower pressure in the air. When a lightning strikes, it rises the temperature around it to about 20.000 degrees Celsius. This extremely hot air creates a pressure wave which comes in contact with the colder air of the surroundings, and thus creates sound waves, which is what we know as thunder.
All this brings us to lightning rods, or lightning conductors. It is obvious that lightning is very dangerous, and being struck by one could be proven fatal. This is why we take the necessary precautions. Lightning rods are considered as an invention of Benjamin Franklin. A lightning rod essentially is a long metal rod, around 2 cm in diameter, which aims to protect a certain structure. This rod is connected with a long wire that leads to a ground rod. It is crucial for the lightning rod to have a connection to the earth, in order to perform its protective action. The rods and the wire are made of conductive materials, such as copper, which would be able to conduct the lightning’s electricity, in case it should strike. If lighting was to hit the structure, it would most probably hit the rod, because the negative step leaders of the cloud would first find in their way the positive streamers of the rod to connect with. Here, it must become clear that, contrary to popular belief, the lightning rod does not attract lightning. It gives the lightning a safe option to pass through, if it were to hit the specific structure, providing a low-resistance path to the ground.
If lightning struck a non-conductive material, it would cause it to burn or be electrocuted. Hitting the lightning rod, however, through its system consisting of conductive materials, it would be safely led to the ground, avoiding any possible damage.
Finally, electricity is one of the most captivating fields of physics, and also one of the most essential factors that form our everyday life as it is. Electricity is everywhere, from the nervous impulses carried in our neural system, allowing us to sense and act, to every technological advance and invention. It is, undeniably, a fascinating field, which, however, may be encountered with dangerous forms, such as the one of lightning. It is, therefore, crucial to take the necessary protections against such life-threatening examples of electricity.
Lewin, W.& Goldstein, W. (2011). For the Love of Physics. N.Y.: Free Press
Zavisa, J. Retrieved from website: https://science.howstuffworks.com/nature/natural-disasters/lightning7.htm