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When to use I²R, V²/R or VI while calculating Electric Power?

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I came across a question that was asked to me quite a couple of time: When to use I²R, V²/R or VI while calculating power? At first, the question looks simple and as if it needs no formal explanation but that's not the case. Use of any of them will give the correct result provided that you apply it correctly. Correct application is possible only when you understand the type of circuit you are dealing with. Another important point is to use the one which is going to take less time and help you calculate easily. All of the three equations tell the same thing but their usage is subject to the type of problem you're trying to solve. Let us understand when, how an what to use while calculating power in an electrical circuit.
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What exactly causes lightning in the clouds and how to avoid them?

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Lightning followed by a thunderbolt is a common phenomenon while it's raining heavily or when it is tending to rain. Lightning strikes are one of the many natural causes common for so many deaths or injuries around the world. About 240,000 cases of lightning strike happen every year around the world and about 6000 people lose their lives every year. As of June 2020, nearly 100-120 people have already lost their lives in northern India due to lightning.
But what induces these lightning strikes? Why they are lethal and common? In this article, I will try to explain the cause of lightning in a simple manner and also how to avoid it.

Lightning is an electrical discharge phenomenon. Any such thing happens between two opposite electrical charges separated by a distance.

The hot air from the ground rises up and cools down to form water and eventually to smaller pieces of ice (due to the freezing temperatures in the upper atmosphere). These water droplets and ice along with the cold air forms cloud. The more the hot air goes up, the bigger will be the cloud. Due to the enormously flowing wind, these pieces of ice plunge into each other at violent speeds causing the formation of electrical charges. Finally, the whole cloud is filled up with the charges, positive and negative.

As positive charges are lighter than the negative charges, the positive charge goes on the upper surface of the cloud and the lower surface of the cloud is filled with negative charges. Hence, the process of sparking or lightning within the cloud begins.

Separation of charges gives rise to a potential difference of several thousand Volts. The dielectric breakdown voltage of the air is 30kV/cm which means if the potential difference between two points in vacuum or in normal atmospheric conditions lying 1 cm apart goes beyond 30kV, the air between them will lose its dielectric strength and will start behaving as a conductor. This is because the breaking of dielectric strength means the generation of free electrons which were forming a covalent bond erstwhile with their respective Nucleus. These free electrons thus behave like electric charge carriers and hence a spark jumps off or in case of the cloud, a bolt of lightning happens.

Now, as the lower surface of the cloud is filled with negative charges, the positive charges from the ground beneath the cloud gets attracted towards the cloud. Anything below the cloud carries these positive charges from the ground, plants, animals, buildings and skyscrapers etc. The one who is tallest among all the things in the surroundings carries the positive charge nearer to the cloud and hence a bolt of lightning jumps off from the cloud onto the object or on the person standing below. That's why it is recommended to stay inside when it's lightning heavily or there are violent clouds roaming around.
 
Before lightning strikes a human body, all the hairs on the body stand straight pointing upwards as they carry the positive charge and attracted to the cloud. It's a signal that he/she can face a lightning strike and that they should immediately hide somewhere except under a tree or anything longer and susceptible to the lightning bolt. Also, sharp and pointed objects shouldn't be directed towards the sky as chances are there and greater that a bolt will fall on the object. If you are in the vicinity of anything longer/sharper, then move away immediately. Even sitting in a car for that matter is one of the safest options.





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