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Category: light and photon
Updated August 02, 2023

Coulomb's equation (1785)

Coulomb's equation (1785)

Image: Named after Charles-Augustin de Coulomb, Coulomb's law (F=kqq/r²) is an equation that represents the attractive or repulsive electric force (F) of two point charges (q).

F = k q₁ q₂ / r²

Coulomb's equation is one of the fundamental laws of electrostatics describing the electrical interaction between electrical charges. This equation is named after the French physicist Charles-Augustin de Coulomb (1736-1806), who formulated it in the 18th century.

Coulomb's equation is mathematically expressed as follows: F = k q₁ q₂ / r²
- F is the electrostatic force between two point electric charges q₁ and q₂.
- k or ke is the Coulomb constant, which depends on the system of units used and the permittivity of the vacuum noted ε₀ (capacity of an empty space to polarize in response to an applied electric field).
- r is the distance between the two charges.

Some key points to remember about this equation

The electrostatic force acts on positive and negative electrical charges, and it can be attractive (between opposite charges) or repulsive (between charges of the same sign).

This force is described by Coulomb's law. Electric charge is expressed in coulombs (C) in the international system of units (SI). Electrons carry a negative elementary charge of approximately -1.602 x 10^-19 C, while protons carry an equal positive charge in absolute terms.

The electrostatic force decreases with the square of the distance between the charges. This means that the farther the loads are apart, the faster the force decreases.

Coulomb's equation is valid for immobile charges in the context of static electricity. If the charges are in motion, the effects of special relativity (magnetism) should be taken into account and Maxwell's equations of electromagnetism should be used.

Through electrostatic force, electrical charges interact and help shape our electrical world.

Electrical phenomena due to electrostatic force

Static electricity is an electrical phenomenon that occurs when stationary electrical charges build up on the surface of an insulating object. Electrical charges are formed when objects are rubbed together, creating sparks or feelings of electric shock.

Lightning is a very powerful electrical natural phenomenon that occurs when there is an electrical discharge between clouds charged with static electricity and the ground or between the clouds themselves.

The Aurora Borealis and Australis are spectacular light displays in the polar regions caused by charged particles from the solar wind colliding with charged particles from Earth's atmosphere.

St. Elmo's fires are luminous phenomena that sometimes occur on sharp objects such as ship masts or the tops of trees during thunderstorms. They are caused by the buildup of electrical charges in the air around these objects.

Ball lightning is floating electric light spheres that can appear during thunderstorms and move erratically.

Atmospheric static electricity is also responsible for the presence of an ion layer in the Earth's ionosphere, which plays an important role in radio communications and electromagnetic wave refraction phenomena.

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