Coulombs Law

A brief introduction to Coulomb’s Law

Coulomb’s Law was one of the greatest derivatives that unified the entire concept of electric field masses and the force produced between them. According to the law, when two charged objects are kept at a certain distance, the force between them would be directly proportional to the multiplied value of both charges and would be inversely proportional to the square of the distance between them. 

This law is also known as the inverse square law due to the fact that the square of the distance between the two charges inversely changes the entire force between two electrically charged objects. The electrostatic force or the force produced by the electric bodies on a static movement is also known as Coulomb’s force. 

It is given by,

F= kq1q2R212

Here  q1 and q2 are the 2 charges and R21 is the distance between them. And k is a constant whose value is given by 9109Nm2/C2

History of Coulomb’s Law

The history of Coulomb’s force and the discovery of electromagnetic charges date back to the early Mediaeval period. People in those days were very keen on different scientific phenomena but were yet to discover their causes.

The discovery of electromagnetic forces or electrostatic forces was not something new and was reported during that time. People observed that when materials, such as fur and rod, were rubbed against each other, they produced a certain amount of attraction and repulsion, also known as the electrostatic force.

In 600 BC, Thales of Miletus was the first-ever man who published an article and wrote about such occurrences when a piece of amber was rubbed. However, people did not believe it had a scientific basis, considering it a magic trick. 

Furthermore, in the late 1600s, the scientist William Gilbert made a discovery and carefully studied the action of electromagnetic charges and electric fields. He carefully studied the amber phenomena. Based on his studies, he further coined the term electricus, which meant amber. He described the property of amber to attract tiny bodies when rubbed. 

Furthermore, when the concept of electricus spread across the English subcontinent, people started to realise more relevant things with the discovery.

It is said that in 1646, Thomas Browne printed the word by mistake, which became more acceptable to people than the original word. The term got simplified, and the term electricity was generally accepted.

In the 18th century, when physicists such as Bernoulli were active, people considered the electric field charge to act similarly to gravity. This led to the concept that these charges were reduced when the distance increased. 

As time passed, more people found the phenomena interesting, and you could get numerous papers predicting the cause of the force and the effect of the force on different bodies. That was until when sir Charles-Augustin de Coulomb finally confirmed everything in 1785  and came with his publication of the so-called three laws of Coulomb’s force. 

This publication was further helpful in the publication of the theory of electromagnetism. He used different concepts and observations regarding the theory. He also used a torsion balance to study the distance and other factors that influence the repulsion attraction of charges and bodies out there. Furthermore, he came up with the fact that the product of the two charges were directly proportional to the force between them. 

Coulomb’s Law in vector form

Understanding the vector form of Coulomb’s Law is very important. But first, you must understand that there are basically two basic physical quantities: scalar and vector quantities.

A scalar quantity is a quantity that only has magnitude and no specific direction regarding its application. On the other hand, if an entity depends on both magnitude and the direction of velocity, it is called a vector form. 

When Coulomb was framing his laws regarding the electrical charge, he found that these laws also had to be written in the vector. This meant that charges that would be multiplied in the formula for producing the force would have to be defined in a specific direction, or the law would fail. 

Now, let’s define Coulomb’s Law in vector form.

Let q1 and q2 be two charges that are going to participate in the law. 

They will have to be placed at R1 and R2, which are two vector positions where these two charges are. 

The vector that must start from q1 to q2 will be termed R21.

The value of R21 = r2 – r1

Coulomb force F= kq1q2R212

Here k is a constant and its values is 9109Nm2/C2

The same would be applied when we talk about the vector form from q2 to q1 but in a vice versa form.

When we include all these factors and points, we will get Coulomb’s Law formula in the vector form.

Characteristics of Coulomb’s Law:

While discovering Coulomb’s law, the scientist himself gave certain characteristic features of this law. These features are:

• This law will only be valid when the charge is at rest. Once the charge starts to move from its position in a certain direction, there will be problems regarding the law’s application.
• Like charges will always repel each other. If an electrostatic force is induced by two such objects with the same charge, such as + and +, these charges will start to repel each other, and the electrostatic force produced will be in the opposite direction.
• Similarly, if the charges are unlike and they’re placed at a certain distance, the electrostatic force developed between them will try to reduce the distance between the charges, and the result would be an attraction of the two bodies. 
• Both the attraction and repulsion force would not act outside the given line. These forces will act on a specific certain line, and both the bodies must follow the force on this given line. 
• The size and the amount of force will directly vary with the electric charge on both bodies and will inversely change with the square of the distance. 
• The law also mentions a constant known as the Coulomb’s constant, which comes in the place of the so-called variability of the charges and distance.

Conclusion

We have tried to mention different aspects and points of Coulomb’s Law and its variation. The law defines the change in the electrostatic force between two bodies at a certain distance. There are various factors and points related to the law that are considered very important. We have mentioned the basic concepts of the law.