Coulomb’s Law

Coulomb’s Law

The study of electrostatics begins with the Coulomb’s law. It is an experimental law published in 1785 by French physicist Charles Augustin de Coulomb. This law is very important for the development of theory of electromagnetism.

Charles Coulomb observed that when two electric charges are placed close to each other, they experience a force. He used a torsion balance to measure the repulsive and attractive forces between charged particles

Statement of Coulomb’s Law: Charles coulomb has developed the two laws on the basis of his experiments, which are known as Coulomb’s law of electrostatics.

Coulomb’s Law of Electrostatics: We begin with the magnitude of the electrostatic force between two-point charges q and Q. It is convenient to label one of these charges, q, as a test charge, and call Q a source charge. As we develop the theory, more source charges will be added. If r is the distance between two charges, then the force of electrostatic formula is:

\(F\,\,=\,\,\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{qQ}{{{r}^{2}}}\,\,=\,\,{{k}_{e}}\frac{qQ}{{{r}^{2}}}\),


Electric Field: Electric field lines are useful for visualizing the electric field. Field lines begin on positive charge and terminate on negative charge. Electric field lines are parallel to the direction of the electric field, and the density of these field lines is a measure of the magnitude of the electric field at any given point.

We show charge with “q” or “Q” and smallest unit charge is 1.6 x 10⁻¹⁹C. One electron and a proton have same amount of charge.

Positively Charged Particles: In this type of particles, numbers of positive ions are larger than the numbers of negative ions. Means, the numbers of protons are larger than the number of electrons. To neutralize positively charged particles, electrons from the surroundings come to this particle until the number of protons and electrons become equal.

Negatively Charged Particles: Similarly, numbers of electrons are larger than the number of protons. To neutralize negatively charged particles, since protons cannot move and cannot come to negatively charged particles, electrons moves to the ground or any other particle around.

Neutral Particles: Include equal numbers of protons and electrons. They have both protons, neutrons and electrons however, numbers of positive ions are equal to the numbers of negative ions.

Electrostatics Examples: There are many examples of electrostatic phenomena, from those as simple as the attraction of the plastic wrap to your hand after you remove it from a package, and the attraction of paper to a charged scale, to the apparently spontaneous explosion of grain silos, the damage of electronic components during manufacturing, and photocopier and laser printer operation.