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Explanation of Coulomb’s Law Physics is one of the important materials in human life that has been studied for centuries in different eras, and one of the most important chapters taught by physics is the electrical charges that are the backbone of modern life that is currently used and we can not do without it, and these studied electrical charges are not only related to electric current Which passes through electric wires and only gives us light, but the principle of electric charges relates to every electronic work we use daily, from computers, smart devices, digital kitchen tools, modern washing machines, printers, and others, thousands of examples, and all of this depends on the laws of physics such as Coulomb’s law, and in In our article today on the reference website, we will learn about the concept of electric charge, explain Coulomb’s law, and mention practical examples of it and everything related to this topic

concept of electric charge

The electric charge is known scientifically as the basic physical property of the material carried by some elementary particles that controls how the particles are affected by the electric or magnetic field. Also with the constant electric charge, and the definition of electric charge can be simplified in a formula that the mind can understand easier. We say, electric charge is the amount of energy or electrons that move from one body to another through different modes such as conduction, induction, or other specific methods.[1]

Research on physics and its importance in our lives

Types of electric charge

The constant in physics is the value that does not change, and among the constants in physics is the type of electric charges possessed by particles of subatomic matter, which are:

  • The positive charge that protons have. When an object has a positive charge, it means that it has more protons than electrons.
  • The negative charge that electrons have. When an object has a negative charge, it means that it has more electrons than protons.
  • The neutral charge which has a value of zero and is possessed by neutrons, when there are an identical number of positive and negative charges, the negative and positive charges cancel each other out and the object becomes neutral.

properties of electric charge

Electric charge has three basic properties that you will mention with a simple illustrative example to better understand them, namely:

  • Electric charge is naturally additive: For example, if we have a system with two charges, q1 and q2, then the total charge of the system will be the algebraic sum of q1 and q2 and weirs of the sum b qn.
  • Electric charge is a conserved quantity: this means that the charge cannot be created or destroyed, but rather can only be transferred from one body to another by certain methods such as conduction and induction, and as a realistic and simple example that can be tried at home, if we rub a glass tube with a cloth, the positive charge will move to it, and if We brought him close to a small piece of paper, and he would attract it to him.
  • The electric charge is quantifiable: This property was proven by Faraday in his experiments published in 1912 AD, which says that the basic unit of charge is the charge carried by the electron or the proton, and this indicates the fact that the charge is a specific quantity and we can express it as integral multiples of the unit basic charge.

Electric charging methods

Charging is the process of supplying the body with an electric charge or extracting the electric charge from this body. An uncharged body can be charged in three different ways:

  • Charging by Friction: This process occurs when two bodies are rubbed against each other so that one body loses its electrons while the other body gains electrons, and the body that loses electrons becomes positively charged and the body that gains electrons becomes negative.
  • Charging by conduction: It is done by bringing an uncharged body close to a charged body, so that the charged conductor contains an unequal number of protons and electrons, and therefore when an uncharged conductor approaches it, it empties electrons to stabilize itself.
  • Charging by induction or induction: The process of charging an uncharged conductor by bringing it close to a charged conductor without any physical contact.

Explanation of Coulomb’s law

Coulomb’s law is defined in a simple way as a mathematical description of the electric force or the electrostatic interaction between charged objects. Between two electrically charged bodies, this law was published and accompanied by a mathematical equation explaining the force that causes the bodies to attract or repel, and this law is known today as Coulomb’s law or Coulomb’s inverse square law.[2]

Coulomb’s law text

This law is similar to Isaac Newton’s law in gravitation, and Coulomb’s law states, according to the French physicist who put it, that the force of attraction or repulsion acting on a straight line between two charged bodies is directly proportional to the product of the product of their charges, and inversely proportional to the square of the distance between them, and this interaction occurs through The process of attraction and repulsion produces the electric force we know.

Coulomb’s law analysis

According to Coulomb’s law, there are three variables that affect the electric force, which are the two charges and the distance between them, and this effect is analyzed according to the following:

  • The direction of the electric force depends on whether charged objects are charged with a similar charge or an opposite charge. If the two charges are negative or positive, they repel each other, while if one is positive and the other negative they are attracted.
  • The attraction or repulsion runs straight along the line separating the two charges, meaning that the two forces do not come into contact.
  • The magnitude of the force varies inversely with the square of the distance between the two charges, this means that if the distance between the two charges is doubled, the property of attraction or repulsion will weaken and decrease to a quarter of the original value, while if the charges are approached by 10 times the magnitude of the force will increase by a factor of 100.
  • The magnitude of the force is proportional to the value of each of the two charges, so if there are two positive charges, one of 0.1 coulomb and the second of 0.2 coulomb, they will repel a force that depends on the product of the first and second charges, i.e. 0.2 x 0.1, and therefore, if both charges are reduced by half , in turn, the repulsion will be reduced to a quarter of its previous value.

What is the coulomb constant?

Coulomb’s constant, or what is physically called 1 Coulomb responsible, is the charge that repels an equal charge of the same sign with a force of 10⁹ × 8.98 Newtons, when the charges are one meter away in a vacuum, a force measured and fixed by the scientist Coulomb, and the Coulomb force is defined on It is the mutual and internal conservative force in the charge, and it is worth noting that Coulomb’s law and Coulomb’s constant are valid only in the case of static charges, ie the static charge.

Mathematical Formula for Coulomb’s Law

The mathematical formula of Coulomb’s law or Coulomb’s law equation, depends on the text of the law itself, which determines the variables and constants in the equation, and its equation is f=k×(q1×q2)/r², and the significance of these symbols according to the text of the law is as follows:

  • Significance f: It expresses the electric force exchanged between the two charges, measured in newtons.
  • Significance of k: It is Coulomb’s constant and its value is 10⁹× 9.0 Newtons.
  • Indication of q1: the amount of the first charge measured in coulombs.
  • Indication q2: The amount of the second charge measured in coulombs.
  • Indication of r²: the square of the distance between the two charges divided in metres.

Limits of Coulomb’s Law

The limits of Coulomb’s law are the cases or conditions in which this law is used, and if these cases change, there are other physical laws. As for these limits, they are:

  • Coulomb’s law applies only to point charges that are at rest, i.e. in the case of stationary charges.
  • This law can only be applied in cases where the inverse square law stipulated in this law is complied with and this is a prerequisite.
  • It is difficult to apply this law when the shipments are arbitrary, due to the inability to determine the distance between shipments, and this condition is very clear in the text of the law.

Solve arithmetic problems using Coulomb’s law

To clarify the law in a more practical way and increase the understanding and application of Coulomb’s law, we will solve some problems under this law with an explanation of the solution. The generally accepted formulas for converting to coulombs are:[3]

  • 1 coulomb = 10⁶ microcoulombs.
  • 1 colum = 10⁹ nano colum.

The first issue

If we assume that we have two point charges, each with a cost of +1.00 coulomb, and these charges are separated by a meter, find the magnitude of the electric force of the repulsion between them.

Solution: This problem is simple, and there are no values ​​that need to be converted, and it includes all the elements required by the solution within the framework of the equation set in Coulomb’s law, which are the two charges and the distance, and therefore the given values ​​can be substituted in the equation of Coulomb’s law, f=k×(q1×q2) /r², directly to solve the problem as follows:



The second issue

Two balloons are charged with the same amount and type of charge -6.25 nanocoulomb, then they are separated from each other at a distance of 61.7 cm, find the magnitude of the electric force of the repulsion between them.

Solution: Before solving the numbers must be converted to their correct units, for example, the charge is subtracted in the nanocoulomb unit and must be converted to coulombs, as well as the distance is subtracted in centimeters and must be converted to meters according to the following:

  • q1 = q2 = -6.25 = -6.25 × 10⁹-
  • r = 61.7 ÷ 100 = 0.617 m

Then we substitute the values ​​into the equation to derive the result and use the appropriate algebraic steps to solve the unknown or unknown information according to the following:

  • F=(10⁹× 9.0)×(6.25×10⁹-)(6.25×10⁹-)/0.617 m².
  • F=9.23 x 10⁹-

The third issue

Two balloons with charges of +3.37°C and -8.21°C are attracted to each other by a force of 0.0626 Newtons. Determine the distance between the balloons.

Solution: Here the unknown value is the distance. Before going into the solution, the units must be converted from microcolumns to coulombs according to the following:

  • q1=3.37+=+3.37×10⁶-
  • q2=8.21-=-8.21×10⁶-

In the following we use the inverse of Coulomb’s law equation to get the distance. If f=k×(q1×q2)/r², then r²=k×q1×q2/f, then the solution according to the inverse of the equation is:

  • r²=(9.0×10⁹)×(+3.37×10⁶-)×(-8.21×10⁶-)/(0.0626).
  • r²=3.98 م2
  • r = 1.99 m

Newton’s third law states that every force

Coulomb’s law applications

Coulomb’s law applications are among the most common applications that we use in our daily lives without realizing it. Below we will present the most commonly used applications in every place we are.[4]

Dissolving substances in water

The greatest example of it is sodium chloride or table salt that we use constantly, as there is an electrostatic interaction between the solute and the solvent. Salt is polar in nature, and for this reason it is attracted to water and dissolves in it easily, while oil is nonpolar in nature, and therefore does not mix with water.

Hair comb or balloon

This is a common process that can be tried at home also quite simply, when combing the hair, the charges are deposited on the comb teeth when rubbing the hair, and if we bring the charged comb close to pieces of paper that are charged with opposite or neutral in nature, the leaves will be attracted to the comb, and the same if we rub a balloon with hair Or a piece of cloth and we bring it close to the wall, it will be attracted to it and get attached to it.

car paint

The paint that is used for car paint is a mixture of polyester and pigments, and when the paint is placed in the spray gun, it is positively charged with the help of an electromagnetic coil, and the piece that is being painted is charged with a negative charge by a wire called the grounding or discharge wire. Between the positively charged and the negatively charged body the paint is deposited evenly on the surface of the body.


Printers consist of three main parts: a hydrogen lamp, a photosensitive drum made of selenium, and a toner drum. Electrostatically removes the document on its surface to rotate and contact with the positively charged toner, and then is attracted to the negatively charged parts of the impression, and here the cylinder transfers the image to the paper to complete the copying process.

Coulomb’s law pdf

Coulomb’s law is one of the most important laws that relate to actual and practical applications related to the things we do today, although this law was developed in the third quarter of the eighteenth century, and due to its importance, we present it to readers as a pdf file that can be downloaded “from here”, to keep A reference that can be referenced easily when needed.

In this way, we reach the end of our article, which was entitled Explanation of Coulomb’s Law, through which we got acquainted with the concept of electric charge and everything related to it.


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