Conclusion

Nowadays, we are able to prevent the dammages of the lightning. Thanks to Benjamin Franklin who worked hard on the lightning rod. he sometimes made mistakes in his analysis. Because it’s human, but that time he worked without safeguard.

Benjamin Franklin was dedicated to his work, to the things he discovered every day. Till now, we use franklin’s lightning rod. Though it has evolved, the lightning rod is the direct legacy of a genius who ran the risk of being burnt or electrified. He was the kind of man who thought Life was extraordinary and limitless, and who dedicated his life to share his discoveries. Indeed he is one of the men who marked the history of the United States. He was even one of the signatories of the constitution.

c) Laws on electricity : Point Power

During the kite experiment, Benjamin Franklin put an iron stalk on the kite. As he wanted to prove the similarities between lightning and electricity, that was an exellent reasoning.

Indeed, a law regarding electricity was discovered after Franklin’s life-time. It tells us the smaller an object is, the stronger its electric field is near it. The law involved is Gauss’ law.

Where E is the value of the electric field in a point near the sphere,

1/(4πε) is a constant ( also called k),

Q the total electric charge of the sphere,

and r the radius from the source to the point.

E(S1)= k*Q*(1/R²)= (k*Q)/(2r)²= (k*Q)/r² * ¼

= ¼ E(S2)

E(S2)= k*Q*(1/r²)= (k*Q)/r²= (k*Q)/r²= 4 E(S1)

E is inversely proportional to r squared

That proves that with a radius twice smaller, S2 owns an electric field 4 times stronger near it.

If we apply that principle to an infinitely small object, its electric field will be infinitely strong near it. And if we identify a point as a small object, its electric field is strongly worth. It is an important factor that allows the ionization of the air particles wich determines the path of the lightning.

Introduction

For a long time, humans have justified the lightning as god’s penalty. Then came the time they wanted to protect themselves from that natural phenomenon.

Benjamin Franklin was born in 1706 in Boston and died in 1790, in Philadelphia. He was a pioneer in the research about the lightning so there weren’t any precedent studies about the similarities between lightning and electricity. He had to lead a typically scientific step to advance the concern. As expected, his first question about the lightning was “What is lightning?” .He had in fact an intuition. Indeed He is the one who discovered the electric nature of the lightning. During the Age of Enlightenment, a century full of discoveries, Franklin’s lightning rod was one of the main inventions and never stopped evolving from 1752 to now.

What we are talking about is the initiative that took an inventor, at the risk of his life, to give out a shield to the humankind. We’ll study the lightning then, its similarities with electricity and Franklin’s legacy in the modern lightning rod.

a)The kite experiment

During summer 1752, in Philadelphia, Benjamin Franklin carry out the kite experiment to prove the similarities between electricity and lightning.

Benjamin Franklin supposed that he could withdraw electricity from a charged body with another point sharped one. So if the clouds are electrified, we could safely discharge them and protect people against lightning disasters.

We are going to explain his arguments with other terms.

(a) There is a separation of electrical charges when the metallic point is isolated.

(b) When the rod is linked to the ground, a steady current is flowing through the rod.

The picture (a) represents a metal rod which is negatively charged at the bottom and isolated under a stormy cloud. The electric field, vertically directed to the bottom, induces a separation of the charges in the rod. The negative charges in the air neutralize some positive charges at the top of the rod. Therefore, it gets negative charges in excess. When a conductor body linked to the ground, as a person, touches the isolated rod, it produces a spark. Whereas in picture (b), when a rod is linked to the ground, the negative charges flow from the rod to the ground. One can see a glimmer at the top of the stick.

Franklin decided to make a kite with two crossed-sticks and a silk handkerchief. He put an iron point on the vertical silk. At the end of the rope, he fixed a key.

During a thunderstorm, he went in the meadow with his son. He sheltered from the rain in a hangar and let the kite. Then, Benjamin Franklin noticed that some wisp of the rode moved away from each other and stiffened. He touched the key and a spark appeared. The phenomenon repeated. He proved then that the clouds are charged and that lightning is an electrical disaster.