
Coulomb's Law, published by French physicist Charles-Augustin de Coulomb in 1785, is a cornerstone of electromagnetism. It states that the magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. Coulomb's Law can be used to determine the electric field, which is the force exerted on a positive test charge by a point charge. The electric field is dependent only on the charge creating it and the distance between the charges. This law is applicable for non-relativistic speeds of the point charge and can be extended to include any number of point charges using the law of superposition.
| Characteristics | Values |
|---|---|
| Coulomb's Law Equation | F = k q1 q2/r^2 |
| Magnitude of Force | F = k q Q /r^2 |
| Electric Field Units | Newtons per Coulomb (N/C) |
| Electric Field Strength | E = F/q |
| Electric Field Vector | Parallel to Force Vector |
| Point Charge | Single charge at rest |
| Gauss's Law | Equivalent to Coulomb's Law for a single point charge |
| Superposition | Applicable to any number of point charges |
| Relativistic Speeds | Coulomb's Law reduces to Electric Field expression |
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What You'll Learn

The inverse proportion of the square of the distance between two charges
Coulomb's law, also known as Coulomb's inverse-square law, is a fundamental principle in physics that describes the relationship between electrically charged particles. It was formulated by French physicist Charles-Augustin de Coulomb in the late 18th century and played a pivotal role in the development of electromagnetism.
Coulomb's law states that the magnitude of the electric 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. This relationship can be expressed mathematically as:
> {\displaystyle \mathbf {E} (\mathbf {r} )={\frac {q}{4\pi \varepsilon _{0}}}{\frac {\mathbf {e} _{r}}{r^{2}}}}
In this equation, 'q' represents the magnitude of the charges, and 'r' represents the distance between them. The constant '4πϵ₀' accounts for the characteristics of the medium in which the charges are placed.
The inverse square relationship in Coulomb's law means that as the distance between two charges increases, the electric force between them decreases rapidly. This is because the electric field strength diminishes with distance, following an inverse square law. Specifically, if you double the distance between two charges, the electric force between them becomes only one-fourth as strong. This principle holds true for both attractive and repulsive forces between charges.
Coulomb's law is analogous to Newton's law of universal gravitation, which also follows an inverse square relationship. However, a key difference is that gravitational forces always result in attraction, whereas electrostatic forces can lead to either attraction or repulsion, depending on the charges involved.
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The magnitude of the electric force between two point charges
Coulomb's law, also known as Coulomb's inverse-square law, is a fundamental principle in physics that describes the electrostatic force between two charged particles at rest. This law was first published in 1785 by French physicist Charles-Augustin de Coulomb, revolutionizing the understanding of electromagnetism.
> {\displaystyle \mathbf {F} ={q_{1}q_{2} \over 4\pi \varepsilon _{0}r^{2}}}
In this equation, F represents the force between the charges, q1, and q2 are the magnitudes of the two charges, ε0 is the vacuum permittivity, and r is the distance between the charges.
Coulomb's law provides valuable insights into the behaviour of charged particles. It reveals that like charges, those with the same sign, repel each other, while unlike charges, those with opposite signs, attract each other. This phenomenon is analogous to Newton's inverse-square law of universal gravitation, but with a key difference: gravitational forces always attract, whereas electrostatic forces can result in either attraction or repulsion.
Additionally, Coulomb's law serves as a foundation for understanding atomic and molecular interactions. It accurately describes the forces between positively charged atomic nuclei and negatively charged electrons, as well as the forces that bind atoms and molecules together to form solids, liquids, and gases. By applying the principle of superposition, Coulomb's law can be extended to systems with multiple charges, making it a versatile tool in the study of electric fields and electrostatic forces.
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The relationship between electrical force and electrical field strength
Coulomb's Law states that the magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. This law is similar to Isaac Newton's inverse-square law of universal gravitation, but with a key difference: gravitational forces always attract, while electrostatic forces can either attract or repel.
The electric field, or E-field, is a physical field that surrounds electrically charged particles, such as electrons. It describes the capacity of charged particles to exert attractive or repulsive forces on another charged object. Charged particles exert attractive forces on each other when their charges are opposite in sign and repel each other when their charges have the same sign. The electric field is defined as a vector field that associates each point in space with the force per unit of charge exerted on an infinitesimal test charge at rest at that point. The SI unit for the electric field is the volt per meter (V/m), also known as newtons per coulomb (N/C).
The relationship between electrical force and electric field strength is described by Coulomb's Law. The electric field is the ratio of the Coulomb force to the test charge. The electrostatic force (F) on any charge (q) can be obtained by multiplying the charge by the electric field (E), or F = qE. The electric field depends only on the charge Q and the distance r, and it is completely independent of the test charge q.
The concept of "lines of force" can be used to visualise the electric field, where the direction of the lines at each point is the same as that of the field. The strength of the field is proportional to the density of the lines. Field lines due to stationary charges originate from positive charges and terminate at negative charges. They enter all good conductors at right angles and never cross or close in on themselves.
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The electrostatic force exerted by a point charge on a test charge
Coulomb's law is an experimental law of physics that calculates the amount of force between two electrically charged particles at rest. It can be used to determine the electric field in cases where the charges are not moving too quickly with respect to each other, and the charges are not accelerating.
> $F=k\frac{\mid{qQ}\mid}{r^2}$
Where:
- F is the electrostatic force
- K is the electrostatic constant
- Q is the magnitude of the test charge
- Q is the magnitude of the point charge
- R is the distance between the charges
The electrostatic force field surrounding a charged object extends out into space in all directions. The electric field created by a point charge can be calculated using the equation:
> $E=k\frac{\left|Q\right|}{{r}^{2}}$
Where:
- E is the electric field vector
- K is the electrostatic constant
- Q is the magnitude of the point charge
- R is the distance from the charge
The electric field vector at a point is parallel to the force vector acting on a positive test charge placed at that point. The magnitude of the electric field is given by the equation:
> $\mathbf{E}=\frac{\mathbf{F}}{q}$
Where:
- E is the electric field vector
- F is the electrostatic force
- Q is the magnitude of the test charge
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The law of superposition
Coulomb's law, published by French physicist Charles-Augustin de Coulomb in 1785, states that the magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. Coulomb's law can be used to find the electric field, which is a vector quantity that describes the force experienced by other charges in the field created by a charged particle.
The principle of superposition allows for the combination of two or more electric fields. In one dimension, electric fields can be combined by adding the magnitudes of the fields if they have the same direction, or subtracting the smaller magnitude from the larger one if they have opposite directions. The resulting net field will point in the direction of the larger field.
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Frequently asked questions
Coulomb's Law states that the magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
Coulomb's Law can be used to find the electric field when the charges have the same sign and the electrostatic force between them causes repulsion, or when the charges have different signs and the force between them causes attraction.
The electric field can be calculated using the equation E = F/q, where E is the electric field, F is the electrostatic force, and q is the charge.
The units of the electric field are newtons per coulomb (N/C).











































