Electrostatic Charge And Coulomb’s Law

Questions You Can Answer After Reading :

  • What is Electrostatic?
  • What is the meaning of Static?
  • What is Charge?
  • What are the types of charge?
  • What is the basic unit of charge?
  • What are the fundamental charged particles?
  • How to charge an object?
  • What is the quantization of charge?
  • How to detect the presence of electric charge?
  • What is Coulomb’s Law?
  • What are the similarities and differences between gravitational force and electrostatic force?
  • what is Inverse Square Law?
  • What are the limitations of Coulomb’s law?
  • What is the Superposition theorem?
  • Nature of forces between two charged particles.
  • Other 10 most important questions.


Everyone is familiar with the fact that when we put off our clothes made of terylene or nylon, a crackling sound is produced. Similarly when a very dry hair is combed with a comb crackling sound is produced. what are the reasons behind these crackling sound? This is due to the fact that the comb and synthetic clothes are strongly electrified due to friction.

In general, when a body is rubbed with another body electric charge is produced. The amount of charge produced depends on the nature of objects and the atmospheric conditions. The presence of an electric charge on a body can be detected with the help of an “Electroscope”.

Electrostatic means “Static Electric”. So Electrostatic is the branch of physics/science that explains how electric objects behave when they are static. So I hope it is well known to all that static means anything at rest (Motionless). Now, what is the meaning of Electric? Here electric defines the subjects related to electrons which is the basic charge particle.


A charge is the property of an object due to which it can exert a force on another object if and only if the other object is also charged. There are two types of charges Positive Charge and Negative Charge. The nature and amount of charge are decided by the number of electrons and protons present on the object.

Fundamental charge particle: Electron and Protons are the fundamental charged particles. Electron and protons both have the same amount of charge but the nature is opposite, electrons have 1.6X10-19 units of negative charge and protons have the same amount of positive charge. In most cases, electrons are responsible for charge in a body since protons are not easily removable from the nucleus of an atom.

How an object can be charged? the answer of this is very simple. Any object can be charged by the transfer of electrons/protons. This can be achieved bye :

  1. Charging by Friction.
  2. Charging by Induction.
  3. Charging by Secondary Emission.
  4. Charging by Heating.
  • When electrons are removed from an object, the object is positively charged.
  • When electrons are added to an object, the object is negatively charged.
  • When protons are removed from an object, the object is negatively charged.
  • When protons are added to an object, the object is positively charged.
  • When the number of electrons is more than protons the object is said to have a negative charge.
  • When the number of protons is more than electrons the object is said to have a positive charge.
  • When the number of electrons and protons are equal, then the object is Neutral which means no charge.

Unit Of Charge:

Unit of Charge is “Coulomb” and it is denoted by “C”. An electron has -1.6X10-19 C o charge and a proton has an equal amount of positive charge.

To produce 1 Coulomb of positive or negative charge on an object the number of electrons that must be transferred is 6.25X1018 .

Quantization Of Charge

Quantization of charge implies that charge can assume only certain discrete values. That is to say, the observed value of electric charge (q/Q) of a particle will be integral multiples of (e) 1.6X10-19 C.

q = ne

Important Points To Remember:

  1. A charge is denoted by Q/q.
  2. e denotes charge on an electron.
  3. p+ denotes charge on a proton.
  4. e = -1.6X10-19 C
  5. p+ = 1.6X10-19 C
  6. 1C = 6.25X1018 eclectrons.

Electrostatic forces

When two or more than two charged particles are at a comparable distance then they exert force on each other, this acting force is called electrostatic force. The strength of the force acting between two particles depends on the number of charges on the particles and the distance between them.

These forces can be attractive or Repulsive depending on the nature of two charges.

Like charges repel each other and Unlike charges attracts each other.

the amount of force is given by Coulomb’s Law.

Inverse Square Law:

In science, an inversesquare law is any scientific law stating that a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity.

Coulomb’s Law

The magnitude of the Electrostatics force of interaction between two point charges is directly proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distances between them.

Superposition Theorem

“The principle of superposition states that every charge in space creates an electric field at point independent of the presence of other charges in that medium. The resultant electric field is a vector sum of the electric field due to individual charges.”

Similarities between electrostatic and gravitational forces:

  1. Both act in a vacuum.
  2. Both are central and conservative.
  3. Both obey an inverse-square law.
  4. Both propagate with finite speed c. 

Differences between electrostatic and gravitational forces:

  1. Electrostatic forces are much stronger than gravitational forces .
  2. Gravitational forces are always attractive in nature, whereas electrostatic forces may be either attractive or repulsive.
  3. Gravitational forces are independent of the medium whereas electrostatic forces depend on the medium.

limitations of Coulomb’s law

  1. Applicable only in cases when inverse law works.
  2. Applicable For Point Charges at Rest
  3. It is Difficult to apply Coulomb’s Law when charges are in an arbitrary shape.

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