# Help me to understand Coulomb's law.

• sphyics
In summary, the Coulombs law in SI system is given by
sphyics
Coulombs law in SI system is given by

from where does the factor 4$$\pi$$ come in.

hi sphyics!

(have an epsilon: ε )

it's because 4πε0r2 = ε0A(r), where A(r) is the surface area of a sphere of radius r

see the pf library on Coulomb's law for more details

Putting it another way you can express the constant as a straightforward k where (k is a constant of the medium) but for many problems 4 pi would appear in the final answer.By expressing the constant as 1/4pi epsilon(which of course is equal to k) the 4 pis would cancel in said problems.Take your choice as to how to express the constant but the 1/4pi epsilon option,although it may look more complicated at first sight,actually works out to be the neater option.

Last edited:
Putting it another way you can express the constant as a straightforward k where (k is a constant of the medium) but for many problems 4 pi would appear in the final answer.By expressing the constant as 1/4pi epsilon(which of course is equal to k) the 4 pis would cancel in said problems.Take your choice as to how to express the constant but the 1/4pi epsilon option,although it may look more complicated at first sight,actually works out to be the neater option.

agree with that, but why the fixation with $4\,\pi$ term in a law.

The best example I can think of:
The speed of light in a vacuum is given by root 1/epsilon zero* mu zero
epsilon zero is an electrical constant of the vacuum(as you know) and mu zero a magnetic constant of the vacuum.If we expressed the constant in Coulombs law as a straightforward k then the equation giving the speed of light would be a bit busier( with its 4 pi) and arguably less elegant.Expressing the constant with the 4 pi just works out easier for the majority(not all) of the problems we do.

## 1. What is Coulomb's law?

Coulomb's law, also known as the law of electrostatics, is a fundamental law in physics that describes the force between two charged particles. It states that the force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

## 2. How does Coulomb's law relate to electric fields?

Coulomb's law is related to electric fields because it describes the force between two charged particles, which is caused by the electric field created by those particles. The strength of the electric field is directly proportional to the magnitude of the charge and inversely proportional to the square of the distance.

## 3. What is the equation for Coulomb's law?

The equation for Coulomb's law is F = k(q1q2)/r2, where F is the force between two charged particles, k is the Coulomb's constant, q1 and q2 are the charges of the particles, and r is the distance between them.

## 4. What is the significance of the Coulomb's constant, k?

The Coulomb's constant, k, is a proportionality constant that relates the force between two charged particles to their charges and the distance between them. Its value is approximately 9 x 109 Nm2/C2. It is an important constant in physics and is used to calculate the strength of the electric field and the magnitude of the force between charged particles.

## 5. How is Coulomb's law used in real-world applications?

Coulomb's law is used in various real-world applications, including electronics, medical devices, and industrial processes. It helps engineers and scientists understand and predict the behavior of electrically charged particles in different systems. For example, it is used in the design of electronic circuits, the operation of medical imaging equipment, and the production of static electricity in industrial processes.

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